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 $106.57   6.346%   $113.3329   $113.33   $113.35   $113.30  
  Purchase #2 $227.54   9.528%   $249.22   $249.22   $249.20   $249.20  
  Purchase #3 $12.73   4.288%   $13.2759   $13.28   $13.30   $13.30  
  Purchase #4 $93.27   4.628%   $97.5865   $97.59   $97.60   $97.60  
  Purchase #5 $103.57   8.394%   $112.2637   $112.26   $112.25   $112.30  
  Purchase #6 $207.95   7.246%   $223.0181   $223.02   $223.00   $223.00  
  Purchase #7 $213.58   6.545%   $227.5588   $227.56   $227.55   $227.60  
  7 purchase totals = $965.21       $1,036.2559   $1,036.26   $1,036.25   $1,036.30