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 $76.46   10.770%   $84.6947   $84.69   $84.70   $84.70  
  Purchase #2 $141.25   13.501%   $160.3202   $160.32   $160.30   $160.30  
  Purchase #3 $154.30   4.191%   $160.7667   $160.77   $160.75   $160.80  
  Purchase #4 $24.47   3.299%   $25.2773   $25.28   $25.30   $25.30  
  Purchase #5 $144.53   3.260%   $149.2417   $149.24   $149.25   $149.20  
  Purchase #6 $236.71   9.569%   $259.3608   $259.36   $259.35   $259.40  
  Purchase #7 $59.89   4.560%   $62.621   $62.62   $62.60   $62.60  
  7 purchase totals = $837.61       $902.2824   $902.28   $902.25   $902.30