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 $249.85   7.350%   $268.214   $268.21   $268.20   $268.20  
  Purchase #2 $21.95   9.309%   $23.9933   $23.99   $24.00   $24.00  
  Purchase #3 $129.86   9.274%   $141.9032   $141.90   $141.90   $141.90  
  Purchase #4 $49.39   10.181%   $54.4184   $54.42   $54.40   $54.40  
  Purchase #5 $125.94   10.826%   $139.5743   $139.57   $139.55   $139.60  
  Purchase #6 $175.58   6.284%   $186.6134   $186.61   $186.60   $186.60  
  Purchase #7 $180.32   7.562%   $193.9558   $193.96   $193.95   $194.00  
  7 purchase totals = $932.89       $1,008.6724   $1,008.66   $1,008.60   $1,008.70