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 $182.49   12.166%   $204.6917   $204.69   $204.70   $204.70  
  Purchase #2 $59.74   9.847%   $65.6226   $65.62   $65.60   $65.60  
  Purchase #3 $15.36   11.697%   $17.1567   $17.16   $17.15   $17.20  
  Purchase #4 $53.63   8.853%   $58.3779   $58.38   $58.40   $58.40  
  Purchase #5 $162.88   6.822%   $173.9917   $173.99   $174.00   $174.00  
  Purchase #6 $231.33   4.809%   $242.4547   $242.45   $242.45   $242.50  
  Purchase #7 $169.73   5.141%   $178.4558   $178.46   $178.45   $178.50  
  7 purchase totals = $875.16       $940.7511   $940.75   $940.75   $940.90