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 $183.61   6.472%   $195.4932   $195.49   $195.50   $195.50  
  Purchase #2 $28.72   13.144%   $32.495   $32.50   $32.50   $32.50  
  Purchase #3 $15.53   13.384%   $17.6085   $17.61   $17.60   $17.60  
  Purchase #4 $232.51   11.590%   $259.4579   $259.46   $259.45   $259.50  
  Purchase #5 $123.94   9.191%   $135.3313   $135.33   $135.35   $135.30  
  Purchase #6 $191.61   4.345%   $199.9355   $199.94   $199.95   $199.90  
  Purchase #7 $81.27   4.635%   $85.0369   $85.04   $85.05   $85.00  
  7 purchase totals = $857.19       $925.3583   $925.37   $925.40   $925.30