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 $171.75   13.526%   $194.9809   $194.98   $195.00   $195.00  
  Purchase #2 $100.87   11.184%   $112.1513   $112.15   $112.15   $112.20  
  Purchase #3 $87.83   7.447%   $94.3707   $94.37   $94.35   $94.40  
  Purchase #4 $141.78   8.204%   $153.4116   $153.41   $153.40   $153.40  
  Purchase #5 $243.71   4.109%   $253.724   $253.72   $253.70   $253.70  
  Purchase #6 $91.94   7.128%   $98.4935   $98.49   $98.50   $98.50  
  Purchase #7 $73.90   4.720%   $77.3881   $77.39   $77.40   $77.40  
  7 purchase totals = $911.78       $984.5201   $984.51   $984.50   $984.60