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 $57.53   4.574%   $60.1614   $60.16   $60.15   $60.20  
  Purchase #2 $57.32   9.672%   $62.864   $62.86   $62.85   $62.90  
  Purchase #3 $93.65   8.301%   $101.4239   $101.42   $101.40   $101.40  
  Purchase #4 $242.83   5.102%   $255.2192   $255.22   $255.20   $255.20  
  Purchase #5 $159.97   6.605%   $170.536   $170.54   $170.55   $170.50  
  Purchase #6 $183.99   11.724%   $205.561   $205.56   $205.55   $205.60  
  Purchase #7 $51.34   13.321%   $58.179   $58.18   $58.20   $58.20  
  7 purchase totals = $846.63       $913.9445   $913.94   $913.90   $914.00