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 $124.95   4.463%   $130.5265   $130.53   $130.55   $130.50  
  Purchase #2 $201.84   11.462%   $224.9749   $224.97   $224.95   $225.00  
  Purchase #3 $58.77   9.763%   $64.5077   $64.51   $64.50   $64.50  
  Purchase #4 $92.73   8.549%   $100.6575   $100.66   $100.65   $100.70  
  Purchase #5 $146.42   3.160%   $151.0469   $151.05   $151.05   $151.00  
  Purchase #6 $5.33   3.266%   $5.5041   $5.50   $5.50   $5.50  
  Purchase #7 $73.27   8.324%   $79.369   $79.37   $79.35   $79.40  
  7 purchase totals = $703.31       $756.5866   $756.59   $756.55   $756.60