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 $232.74   7.283%   $249.6905   $249.69   $249.70   $249.70  
  Purchase #2 $216.35   5.855%   $229.0173   $229.02   $229.00   $229.00  
  Purchase #3 $82.43   8.611%   $89.528   $89.53   $89.55   $89.50  
  Purchase #4 $30.66   4.386%   $32.0047   $32.00   $32.00   $32.00  
  Purchase #5 $19.76   7.748%   $21.291   $21.29   $21.30   $21.30  
  Purchase #6 $16.75   9.236%   $18.297   $18.30   $18.30   $18.30  
  Purchase #7 $163.26   7.217%   $175.0425   $175.04   $175.05   $175.00  
  7 purchase totals = $761.95       $814.8710   $814.87   $814.90   $814.80