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 $67.88   12.297%   $76.2272   $76.23   $76.25   $76.20  
  Purchase #2 $241.76   13.711%   $274.9077   $274.91   $274.90   $274.90  
  Purchase #3 $90.39   4.591%   $94.5398   $94.54   $94.55   $94.50  
  Purchase #4 $10.84   5.833%   $11.4723   $11.47   $11.45   $11.50  
  Purchase #5 $57.28   12.504%   $64.4423   $64.44   $64.45   $64.40  
  Purchase #6 $179.83   7.407%   $193.15   $193.15   $193.15   $193.20  
  Purchase #7 $35.28   12.787%   $39.7913   $39.79   $39.80   $39.80  
  7 purchase totals = $683.26       $754.5306   $754.53   $754.55   $754.50