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 $36.43   13.236%   $41.2519   $41.25   $41.25   $41.30  
  Purchase #2 $59.31   8.659%   $64.4457   $64.45   $64.45   $64.40  
  Purchase #3 $88.76   11.752%   $99.1911   $99.19   $99.20   $99.20  
  Purchase #4 $174.90   5.228%   $184.0438   $184.04   $184.05   $184.00  
  Purchase #5 $145.83   9.605%   $159.837   $159.84   $159.85   $159.80  
  Purchase #6 $171.62   10.126%   $188.9982   $189.00   $189.00   $189.00  
  Purchase #7 $81.79   3.443%   $84.606   $84.61   $84.60   $84.60  
  7 purchase totals = $758.64       $822.3737   $822.38   $822.40   $822.30