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 $233.87   13.204%   $264.7502   $264.75   $264.75   $264.80  
  Purchase #2 $18.32   10.271%   $20.2016   $20.20   $20.20   $20.20  
  Purchase #3 $71.50   6.427%   $76.0953   $76.10   $76.10   $76.10  
  Purchase #4 $7.87   9.874%   $8.6471   $8.65   $8.65   $8.60  
  Purchase #5 $65.60   11.858%   $73.3788   $73.38   $73.40   $73.40  
  Purchase #6 $38.91   9.648%   $42.664   $42.66   $42.65   $42.70  
  Purchase #7 $231.35   4.149%   $240.9487   $240.95   $240.95   $240.90  
  7 purchase totals = $667.42       $726.6857   $726.69   $726.70   $726.70