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 $29.75   11.733%   $33.2406   $33.24   $33.25   $33.20  
  Purchase #2 $236.71   9.829%   $259.9762   $259.98   $260.00   $260.00  
  Purchase #3 $36.28   3.519%   $37.5567   $37.56   $37.55   $37.60  
  Purchase #4 $154.93   3.823%   $160.853   $160.85   $160.85   $160.90  
  Purchase #5 $180.37   4.540%   $188.5588   $188.56   $188.55   $188.60  
  Purchase #6 $211.82   11.377%   $235.9188   $235.92   $235.90   $235.90  
  Purchase #7 $57.81   5.153%   $60.7889   $60.79   $60.80   $60.80  
  7 purchase totals = $907.67       $976.8930   $976.90   $976.90   $977.00