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 $229.47   13.709%   $260.928   $260.93   $260.95   $260.90  
  Purchase #2 $117.29   13.695%   $133.3529   $133.35   $133.35   $133.40  
  Purchase #3 $178.46   4.621%   $186.7066   $186.71   $186.70   $186.70  
  Purchase #4 $57.75   5.510%   $60.932   $60.93   $60.95   $60.90  
  Purchase #5 $126.79   3.825%   $131.6397   $131.64   $131.65   $131.60  
  Purchase #6 $141.69   5.130%   $148.9587   $148.96   $148.95   $149.00  
  Purchase #7 $207.61   10.465%   $229.3364   $229.34   $229.35   $229.30  
  7 purchase totals = $1,059.06       $1,151.8543   $1,151.86   $1,151.90   $1,151.80