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 $57.68   11.457%   $64.2884   $64.29   $64.30   $64.30  
  Purchase #2 $211.54   10.761%   $234.3038   $234.30   $234.30   $234.30  
  Purchase #3 $123.32   4.380%   $128.7214   $128.72   $128.70   $128.70  
  Purchase #4 $67.88   13.360%   $76.9488   $76.95   $76.95   $76.90  
  Purchase #5 $26.96   4.514%   $28.177   $28.18   $28.20   $28.20  
  Purchase #6 $78.57   12.147%   $88.1139   $88.11   $88.10   $88.10  
  Purchase #7 $119.36   11.577%   $133.1783   $133.18   $133.20   $133.20  
  7 purchase totals = $685.31       $753.7316   $753.73   $753.75   $753.70