Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $46.85   10.152%   $51.6062   $51.61   $51.60   $51.60  
  Purchase #2 $138.27   5.382%   $145.7117   $145.71   $145.70   $145.70  
  Purchase #3 $132.29   6.172%   $140.4549   $140.45   $140.45   $140.50  
  Purchase #4 $217.82   5.868%   $230.6017   $230.60   $230.60   $230.60  
  Purchase #5 $101.69   5.834%   $107.6226   $107.62   $107.60   $107.60  
  Purchase #6 $159.67   8.771%   $173.6747   $173.67   $173.65   $173.70  
  Purchase #7 $248.39   5.477%   $261.9943   $261.99   $262.00   $262.00  
  7 purchase totals = $1,044.98       $1,111.6661   $1,111.65   $1,111.60   $1,111.70