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 $43.89   13.763%   $49.9306   $49.93   $49.95   $49.90  
  Purchase #2 $160.86   5.593%   $169.8569   $169.86   $169.85   $169.90  
  Purchase #3 $232.45   13.872%   $264.6955   $264.70   $264.70   $264.70  
  Purchase #4 $172.73   7.849%   $186.2876   $186.29   $186.30   $186.30  
  Purchase #5 $249.53   5.414%   $263.0396   $263.04   $263.05   $263.00  
  Purchase #6 $146.51   11.141%   $162.8327   $162.83   $162.85   $162.80  
  Purchase #7 $172.94   9.650%   $189.6287   $189.63   $189.65   $189.60  
  7 purchase totals = $1,178.91       $1,286.2716   $1,286.28   $1,286.35   $1,286.20