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 $233.62   13.373%   $264.862   $264.86   $264.85   $264.90  
  Purchase #2 $164.34   8.710%   $178.654   $178.65   $178.65   $178.70  
  Purchase #3 $11.25   4.430%   $11.7484   $11.75   $11.75   $11.70  
  Purchase #4 $146.33   3.104%   $150.8721   $150.87   $150.85   $150.90  
  Purchase #5 $159.25   7.189%   $170.6985   $170.70   $170.70   $170.70  
  Purchase #6 $184.51   13.181%   $208.8303   $208.83   $208.85   $208.80  
  Purchase #7 $55.38   5.355%   $58.3456   $58.35   $58.35   $58.30  
  7 purchase totals = $954.68       $1,044.0109   $1,044.01   $1,044.00   $1,044.00