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 $233.78   13.218%   $264.681   $264.68   $264.70   $264.70  
  Purchase #2 $118.28   6.223%   $125.6406   $125.64   $125.65   $125.60  
  Purchase #3 $213.85   3.465%   $221.2599   $221.26   $221.25   $221.30  
  Purchase #4 $25.34   9.198%   $27.6708   $27.67   $27.65   $27.70  
  Purchase #5 $119.30   9.184%   $130.2565   $130.26   $130.25   $130.30  
  Purchase #6 $146.71   10.289%   $161.805   $161.81   $161.80   $161.80  
  Purchase #7 $208.80   9.726%   $229.1079   $229.11   $229.10   $229.10  
  7 purchase totals = $1,066.06       $1,160.4217   $1,160.43   $1,160.40   $1,160.50