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 $75.88   6.766%   $81.014   $81.01   $81.00   $81.00  
  Purchase #2 $195.78   5.201%   $205.9625   $205.96   $205.95   $206.00  
  Purchase #3 $203.76   8.770%   $221.6298   $221.63   $221.65   $221.60  
  Purchase #4 $116.86   7.488%   $125.6105   $125.61   $125.60   $125.60  
  Purchase #5 $93.86   6.724%   $100.1711   $100.17   $100.15   $100.20  
  Purchase #6 $48.66   10.221%   $53.6335   $53.63   $53.65   $53.60  
  Purchase #7 $5.28   3.299%   $5.4542   $5.45   $5.45   $5.50  
  7 purchase totals = $740.08       $793.4756   $793.46   $793.45   $793.50