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 $94.26   4.480%   $98.4828   $98.48   $98.50   $98.50  
  Purchase #2 $88.37   4.853%   $92.6586   $92.66   $92.65   $92.70  
  Purchase #3 $90.56   12.836%   $102.1843   $102.18   $102.20   $102.20  
  Purchase #4 $83.30   9.473%   $91.191   $91.19   $91.20   $91.20  
  Purchase #5 $189.51   8.711%   $206.0182   $206.02   $206.00   $206.00  
  Purchase #6 $153.37   11.555%   $171.0919   $171.09   $171.10   $171.10  
  Purchase #7 $23.87   11.518%   $26.6193   $26.62   $26.60   $26.60  
  7 purchase totals = $723.24       $788.2461   $788.24   $788.25   $788.30