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 $65.98   11.422%   $73.5162   $73.52   $73.50   $73.50  
  Purchase #2 $101.88   10.255%   $112.3278   $112.33   $112.35   $112.30  
  Purchase #3 $193.57   11.861%   $216.5293   $216.53   $216.55   $216.50  
  Purchase #4 $162.49   7.367%   $174.4606   $174.46   $174.45   $174.50  
  Purchase #5 $66.49   13.144%   $75.2294   $75.23   $75.25   $75.20  
  Purchase #6 $140.43   12.112%   $157.4389   $157.44   $157.45   $157.40  
  Purchase #7 $152.63   6.712%   $162.8745   $162.87   $162.85   $162.90  
  7 purchase totals = $883.47       $972.3767   $972.38   $972.40   $972.30