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 $53.84   8.255%   $58.2845   $58.28   $58.30   $58.30  
  Purchase #2 $114.43   4.162%   $119.1926   $119.19   $119.20   $119.20  
  Purchase #3 $27.27   7.339%   $29.2713   $29.27   $29.25   $29.30  
  Purchase #4 $184.34   11.724%   $205.952   $205.95   $205.95   $206.00  
  Purchase #5 $156.80   7.537%   $168.618   $168.62   $168.60   $168.60  
  Purchase #6 $244.25   12.756%   $275.4065   $275.41   $275.40   $275.40  
  Purchase #7 $58.91   11.226%   $65.5232   $65.52   $65.50   $65.50  
  7 purchase totals = $839.84       $922.2481   $922.24   $922.20   $922.30