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 $200.66   3.199%   $207.0791   $207.08   $207.10   $207.10  
  Purchase #2 $227.89   9.401%   $249.3139   $249.31   $249.30   $249.30  
  Purchase #3 $54.87   6.214%   $58.2796   $58.28   $58.30   $58.30  
  Purchase #4 $60.26   13.721%   $68.5283   $68.53   $68.55   $68.50  
  Purchase #5 $151.68   8.712%   $164.8944   $164.89   $164.90   $164.90  
  Purchase #6 $191.31   4.259%   $199.4579   $199.46   $199.45   $199.50  
  Purchase #7 $149.68   6.238%   $159.017   $159.02   $159.00   $159.00  
  7 purchase totals = $1,036.35       $1,106.5702   $1,106.57   $1,106.60   $1,106.60