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 $33.30   8.716%   $36.2024   $36.20   $36.20   $36.20  
  Purchase #2 $143.79   3.807%   $149.2641   $149.26   $149.25   $149.30  
  Purchase #3 $105.43   13.433%   $119.5924   $119.59   $119.60   $119.60  
  Purchase #4 $145.64   5.571%   $153.7536   $153.75   $153.75   $153.80  
  Purchase #5 $153.39   4.607%   $160.4567   $160.46   $160.45   $160.50  
  Purchase #6 $200.44   7.871%   $216.2166   $216.22   $216.20   $216.20  
  Purchase #7 $116.87   8.448%   $126.7432   $126.74   $126.75   $126.70  
  7 purchase totals = $898.86       $962.2290   $962.22   $962.20   $962.30