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 $173.69   11.603%   $193.8433   $193.84   $193.85   $193.80  
  Purchase #2 $97.65   13.120%   $110.4617   $110.46   $110.45   $110.50  
  Purchase #3 $157.76   13.390%   $178.8841   $178.88   $178.90   $178.90  
  Purchase #4 $90.78   4.138%   $94.5365   $94.54   $94.55   $94.50  
  Purchase #5 $77.97   7.798%   $84.0501   $84.05   $84.05   $84.10  
  Purchase #6 $138.74   13.469%   $157.4269   $157.43   $157.45   $157.40  
  Purchase #7 $127.92   6.646%   $136.4216   $136.42   $136.40   $136.40  
  7 purchase totals = $864.51       $955.6242   $955.62   $955.65   $955.60