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 $239.94   11.461%   $267.4395   $267.44   $267.45   $267.40  
  Purchase #2 $125.44   8.559%   $136.1764   $136.18   $136.20   $136.20  
  Purchase #3 $70.76   10.525%   $78.2075   $78.21   $78.20   $78.20  
  Purchase #4 $154.38   11.468%   $172.0843   $172.08   $172.10   $172.10  
  Purchase #5 $166.45   4.387%   $173.7522   $173.75   $173.75   $173.80  
  Purchase #6 $23.95   4.605%   $25.0529   $25.05   $25.05   $25.10  
  Purchase #7 $173.73   13.237%   $196.7266   $196.73   $196.75   $196.70  
  7 purchase totals = $954.65       $1,049.4394   $1,049.44   $1,049.50   $1,049.50