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 $83.58   10.589%   $92.4303   $92.43   $92.45   $92.40  
  Purchase #2 $81.73   11.804%   $91.3774   $91.38   $91.40   $91.40  
  Purchase #3 $178.26   8.776%   $193.9041   $193.90   $193.90   $193.90  
  Purchase #4 $140.68   6.175%   $149.367   $149.37   $149.35   $149.40  
  Purchase #5 $210.83   8.144%   $228   $228.00   $228.00   $228.00  
  Purchase #6 $64.98   6.783%   $69.3876   $69.39   $69.40   $69.40  
  Purchase #7 $20.41   5.192%   $21.4697   $21.47   $21.45   $21.50  
  7 purchase totals = $780.47       $845.9361   $845.94   $845.95   $846.00