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 $87.39   12.177%   $98.0315   $98.03   $98.05   $98.00  
  Purchase #2 $194.68   5.628%   $205.6366   $205.64   $205.65   $205.60  
  Purchase #3 $127.32   3.671%   $131.9939   $131.99   $132.00   $132.00  
  Purchase #4 $161.95   10.347%   $178.707   $178.71   $178.70   $178.70  
  Purchase #5 $224.48   8.253%   $243.0063   $243.01   $243.00   $243.00  
  Purchase #6 $221.48   12.561%   $249.3001   $249.30   $249.30   $249.30  
  Purchase #7 $195.48   13.829%   $222.5129   $222.51   $222.50   $222.50  
  7 purchase totals = $1,212.78       $1,329.1883   $1,329.19   $1,329.20   $1,329.10