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 $82.66   12.527%   $93.0148   $93.01   $93.00   $93.00  
  Purchase #2 $231.89   9.516%   $253.9567   $253.96   $253.95   $254.00  
  Purchase #3 $151.57   7.175%   $162.4451   $162.45   $162.45   $162.40  
  Purchase #4 $224.38   13.271%   $254.1575   $254.16   $254.15   $254.20  
  Purchase #5 $60.89   9.113%   $66.4389   $66.44   $66.45   $66.40  
  Purchase #6 $125.78   13.359%   $142.583   $142.58   $142.60   $142.60  
  Purchase #7 $245.92   8.430%   $266.6511   $266.65   $266.65   $266.70  
  7 purchase totals = $1,123.09       $1,239.2471   $1,239.25   $1,239.25   $1,239.30