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 $157.86   7.293%   $169.3727   $169.37   $169.35   $169.40  
  Purchase #2 $239.99   4.669%   $251.1951   $251.20   $251.20   $251.20  
  Purchase #3 $93.96   5.548%   $99.1729   $99.17   $99.15   $99.20  
  Purchase #4 $29.63   11.809%   $33.129   $33.13   $33.15   $33.10  
  Purchase #5 $31.44   11.336%   $35.004   $35.00   $35.00   $35.00  
  Purchase #6 $87.56   7.769%   $94.3625   $94.36   $94.35   $94.40  
  Purchase #7 $248.99   12.605%   $280.3752   $280.38   $280.40   $280.40  
  7 purchase totals = $889.43       $962.6114   $962.61   $962.60   $962.70