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 $46.81   6.564%   $49.8826   $49.88   $49.90   $49.90  
  Purchase #2 $93.71   8.551%   $101.7231   $101.72   $101.70   $101.70  
  Purchase #3 $107.40   4.302%   $112.0203   $112.02   $112.00   $112.00  
  Purchase #4 $226.63   7.672%   $244.0171   $244.02   $244.00   $244.00  
  Purchase #5 $7.47   4.602%   $7.8138   $7.81   $7.80   $7.80  
  Purchase #6 $119.41   5.326%   $125.7698   $125.77   $125.75   $125.80  
  Purchase #7 $32.62   5.146%   $34.2986   $34.30   $34.30   $34.30  
  7 purchase totals = $634.05       $675.5253   $675.52   $675.45   $675.50