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 $175.66   13.268%   $198.9666   $198.97   $198.95   $199.00  
  Purchase #2 $63.25   7.122%   $67.7547   $67.75   $67.75   $67.80  
  Purchase #3 $61.55   4.460%   $64.2951   $64.30   $64.30   $64.30  
  Purchase #4 $136.64   11.212%   $151.9601   $151.96   $151.95   $152.00  
  Purchase #5 $164.53   5.316%   $173.2764   $173.28   $173.30   $173.30  
  Purchase #6 $14.50   8.814%   $15.778   $15.78   $15.80   $15.80  
  Purchase #7 $102.31   6.740%   $109.2057   $109.21   $109.20   $109.20  
  7 purchase totals = $718.44       $781.2366   $781.25   $781.25   $781.40