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 $53.80   12.288%   $60.4109   $60.41   $60.40   $60.40  
  Purchase #2 $191.43   10.241%   $211.0343   $211.03   $211.05   $211.00  
  Purchase #3 $29.63   10.517%   $32.7462   $32.75   $32.75   $32.70  
  Purchase #4 $127.66   7.315%   $136.9983   $137.00   $137.00   $137.00  
  Purchase #5 $70.49   6.747%   $75.246   $75.25   $75.25   $75.20  
  Purchase #6 $35.25   5.838%   $37.3079   $37.31   $37.30   $37.30  
  Purchase #7 $245.88   5.104%   $258.4297   $258.43   $258.45   $258.40  
  7 purchase totals = $754.14       $812.1733   $812.18   $812.20   $812.00