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 $177.49   11.519%   $197.9351   $197.94   $197.95   $197.90  
  Purchase #2 $108.53   10.320%   $119.7303   $119.73   $119.75   $119.70  
  Purchase #3 $78.25   10.237%   $86.2605   $86.26   $86.25   $86.30  
  Purchase #4 $205.42   5.326%   $216.3607   $216.36   $216.35   $216.40  
  Purchase #5 $75.87   11.794%   $84.8181   $84.82   $84.80   $84.80  
  Purchase #6 $113.58   7.130%   $121.6783   $121.68   $121.70   $121.70  
  Purchase #7 $68.99   11.504%   $76.9266   $76.93   $76.95   $76.90  
  7 purchase totals = $828.13       $903.7096   $903.72   $903.75   $903.70