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 $192.81   5.360%   $203.1446   $203.14   $203.15   $203.10  
  Purchase #2 $104.66   11.214%   $116.3966   $116.40   $116.40   $116.40  
  Purchase #3 $122.95   3.154%   $126.8278   $126.83   $126.85   $126.80  
  Purchase #4 $184.46   6.460%   $196.3761   $196.38   $196.40   $196.40  
  Purchase #5 $97.26   4.109%   $101.2564   $101.26   $101.25   $101.30  
  Purchase #6 $112.61   6.802%   $120.2697   $120.27   $120.25   $120.30  
  Purchase #7 $144.62   10.255%   $159.4508   $159.45   $159.45   $159.50  
  7 purchase totals = $959.37       $1,023.7220   $1,023.73   $1,023.75   $1,023.80