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 $190.89   3.711%   $197.9739   $197.97   $197.95   $198.00  
  Purchase #2 $226.75   3.318%   $234.2736   $234.27   $234.25   $234.30  
  Purchase #3 $173.29   7.844%   $186.8829   $186.88   $186.90   $186.90  
  Purchase #4 $45.95   11.461%   $51.2163   $51.22   $51.20   $51.20  
  Purchase #5 $81.47   5.177%   $85.6877   $85.69   $85.70   $85.70  
  Purchase #6 $128.88   4.568%   $134.7672   $134.77   $134.75   $134.80  
  Purchase #7 $128.86   11.580%   $143.782   $143.78   $143.80   $143.80  
  7 purchase totals = $976.09       $1,034.5836   $1,034.58   $1,034.55   $1,034.70