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 $59.38   7.420%   $63.786   $63.79   $63.80   $63.80  
  Purchase #2 $84.42   13.558%   $95.8657   $95.87   $95.85   $95.90  
  Purchase #3 $152.92   7.759%   $164.7851   $164.79   $164.80   $164.80  
  Purchase #4 $61.27   5.632%   $64.7207   $64.72   $64.70   $64.70  
  Purchase #5 $188.88   4.454%   $197.2927   $197.29   $197.30   $197.30  
  Purchase #6 $107.34   4.503%   $112.1735   $112.17   $112.15   $112.20  
  Purchase #7 $241.81   13.456%   $274.348   $274.35   $274.35   $274.30  
  7 purchase totals = $896.02       $972.9717   $972.98   $972.95   $973.00