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 $126.92   6.795%   $135.5442   $135.54   $135.55   $135.50  
  Purchase #2 $59.27   4.179%   $61.7469   $61.75   $61.75   $61.70  
  Purchase #3 $195.72   4.205%   $203.95   $203.95   $203.95   $204.00  
  Purchase #4 $96.56   9.292%   $105.5324   $105.53   $105.55   $105.50  
  Purchase #5 $58.69   11.636%   $65.5192   $65.52   $65.50   $65.50  
  Purchase #6 $208.86   11.743%   $233.3864   $233.39   $233.40   $233.40  
  Purchase #7 $15.46   10.413%   $17.0698   $17.07   $17.05   $17.10  
  7 purchase totals = $761.48       $822.7489   $822.75   $822.75   $822.70