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 $229.58   13.336%   $260.1968   $260.20   $260.20   $260.20  
  Purchase #2 $243.25   6.239%   $258.4264   $258.43   $258.45   $258.40  
  Purchase #3 $84.97   8.685%   $92.3496   $92.35   $92.35   $92.30  
  Purchase #4 $83.98   6.607%   $89.5286   $89.53   $89.55   $89.50  
  Purchase #5 $55.67   8.123%   $60.1921   $60.19   $60.20   $60.20  
  Purchase #6 $21.78   6.557%   $23.2081   $23.21   $23.20   $23.20  
  Purchase #7 $125.62   13.443%   $142.5071   $142.51   $142.50   $142.50  
  7 purchase totals = $844.85       $926.4087   $926.42   $926.45   $926.30