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 $70.44   4.674%   $73.7324   $73.73   $73.75   $73.70  
  Purchase #2 $163.92   12.763%   $184.8411   $184.84   $184.85   $184.80  
  Purchase #3 $160.76   5.398%   $169.4378   $169.44   $169.45   $169.40  
  Purchase #4 $20.63   12.397%   $23.1875   $23.19   $23.20   $23.20  
  Purchase #5 $247.43   11.369%   $275.5603   $275.56   $275.55   $275.60  
  Purchase #6 $87.75   5.555%   $92.6245   $92.62   $92.60   $92.60  
  Purchase #7 $33.62   3.804%   $34.8989   $34.90   $34.90   $34.90  
  7 purchase totals = $784.55       $854.2825   $854.28   $854.30   $854.20