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 $21.32   4.412%   $22.2606   $22.26   $22.25   $22.30  
  Purchase #2 $244.88   4.854%   $256.7665   $256.77   $256.75   $256.80  
  Purchase #3 $7.25   12.680%   $8.1693   $8.17   $8.15   $8.20  
  Purchase #4 $116.82   6.215%   $124.0804   $124.08   $124.10   $124.10  
  Purchase #5 $101.55   11.402%   $113.1287   $113.13   $113.15   $113.10  
  Purchase #6 $134.30   12.698%   $151.3534   $151.35   $151.35   $151.40  
  Purchase #7 $191.73   8.600%   $208.2188   $208.22   $208.20   $208.20  
  7 purchase totals = $817.85       $883.9777   $883.98   $883.95   $884.10