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 $56.36   8.852%   $61.349   $61.35   $61.35   $61.30  
  Purchase #2 $23.32   11.213%   $25.9349   $25.93   $25.95   $25.90  
  Purchase #3 $51.68   4.802%   $54.1617   $54.16   $54.15   $54.20  
  Purchase #4 $64.41   10.826%   $71.383   $71.38   $71.40   $71.40  
  Purchase #5 $210.61   10.798%   $233.3517   $233.35   $233.35   $233.40  
  Purchase #6 $248.57   11.756%   $277.7919   $277.79   $277.80   $277.80  
  Purchase #7 $44.72   5.435%   $47.1505   $47.15   $47.15   $47.20  
  7 purchase totals = $699.67       $771.1227   $771.11   $771.15   $771.20