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 $146.85   10.134%   $161.7318   $161.73   $161.75   $161.70  
  Purchase #2 $244.98   9.761%   $268.8925   $268.89   $268.90   $268.90  
  Purchase #3 $154.70   9.672%   $169.6626   $169.66   $169.65   $169.70  
  Purchase #4 $64.77   12.407%   $72.806   $72.81   $72.80   $72.80  
  Purchase #5 $175.48   4.657%   $183.6521   $183.65   $183.65   $183.70  
  Purchase #6 $62.75   6.723%   $66.9687   $66.97   $66.95   $67.00  
  Purchase #7 $12.54   7.184%   $13.4409   $13.44   $13.45   $13.40  
  7 purchase totals = $862.07       $937.1546   $937.15   $937.15   $937.20