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 $41.91   10.479%   $46.3017   $46.30   $46.30   $46.30  
  Purchase #2 $29.34   12.134%   $32.9001   $32.90   $32.90   $32.90  
  Purchase #3 $53.69   9.251%   $58.6569   $58.66   $58.65   $58.70  
  Purchase #4 $69.41   8.612%   $75.3876   $75.39   $75.40   $75.40  
  Purchase #5 $81.66   7.163%   $87.5093   $87.51   $87.50   $87.50  
  Purchase #6 $221.60   12.624%   $249.5748   $249.57   $249.55   $249.60  
  Purchase #7 $46.93   4.397%   $48.9935   $48.99   $49.00   $49.00  
  7 purchase totals = $544.54       $599.3239   $599.32   $599.30   $599.40