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 $82.25   7.389%   $88.3275   $88.33   $88.35   $88.30  
  Purchase #2 $21.85   11.154%   $24.2871   $24.29   $24.30   $24.30  
  Purchase #3 $140.91   7.691%   $151.7474   $151.75   $151.75   $151.70  
  Purchase #4 $237.31   6.693%   $253.1932   $253.19   $253.20   $253.20  
  Purchase #5 $129.67   12.848%   $146.33   $146.33   $146.35   $146.30  
  Purchase #6 $224.33   11.328%   $249.7421   $249.74   $249.75   $249.70  
  Purchase #7 $68.96   6.377%   $73.3576   $73.36   $73.35   $73.40  
  7 purchase totals = $905.28       $986.9849   $986.99   $987.05   $986.90