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 $203.62   13.758%   $231.634   $231.63   $231.65   $231.60  
  Purchase #2 $51.35   5.347%   $54.0957   $54.10   $54.10   $54.10  
  Purchase #3 $127.25   4.166%   $132.5512   $132.55   $132.55   $132.60  
  Purchase #4 $23.52   13.817%   $26.7698   $26.77   $26.75   $26.80  
  Purchase #5 $153.93   13.209%   $174.2626   $174.26   $174.25   $174.30  
  Purchase #6 $212.38   13.586%   $241.2339   $241.23   $241.25   $241.20  
  Purchase #7 $112.34   5.169%   $118.1469   $118.15   $118.15   $118.10  
  7 purchase totals = $884.39       $978.6941   $978.69   $978.70   $978.70