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 $53.83   7.742%   $57.9975   $58.00   $58.00   $58.00  
  Purchase #2 $161.68   12.441%   $181.7946   $181.79   $181.80   $181.80  
  Purchase #3 $232.28   12.728%   $261.8446   $261.84   $261.85   $261.80  
  Purchase #4 $231.76   11.245%   $257.8214   $257.82   $257.80   $257.80  
  Purchase #5 $103.65   9.342%   $113.333   $113.33   $113.35   $113.30  
  Purchase #6 $95.53   3.264%   $98.6481   $98.65   $98.65   $98.60  
  Purchase #7 $164.39   10.654%   $181.9041   $181.90   $181.90   $181.90  
  7 purchase totals = $1,043.12       $1,153.3433   $1,153.33   $1,153.35   $1,153.20