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 $156.71   3.562%   $162.292   $162.29   $162.30   $162.30  
  Purchase #2 $111.90   12.230%   $125.5854   $125.59   $125.60   $125.60  
  Purchase #3 $18.57   7.310%   $19.9275   $19.93   $19.95   $19.90  
  Purchase #4 $137.70   7.512%   $148.044   $148.04   $148.05   $148.00  
  Purchase #5 $19.31   5.525%   $20.3769   $20.38   $20.40   $20.40  
  Purchase #6 $182.64   12.199%   $204.9203   $204.92   $204.90   $204.90  
  Purchase #7 $231.60   3.576%   $239.882   $239.88   $239.90   $239.90  
  7 purchase totals = $858.43       $921.0281   $921.03   $921.10   $921.00