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 $219.66   11.283%   $244.4442   $244.44   $244.45   $244.40  
  Purchase #2 $239.39   9.601%   $262.3738   $262.37   $262.35   $262.40  
  Purchase #3 $111.49   4.401%   $116.3967   $116.40   $116.40   $116.40  
  Purchase #4 $53.95   7.301%   $57.8889   $57.89   $57.90   $57.90  
  Purchase #5 $37.45   7.181%   $40.1393   $40.14   $40.15   $40.10  
  Purchase #6 $173.88   3.808%   $180.5014   $180.50   $180.50   $180.50  
  Purchase #7 $106.99   12.352%   $120.2054   $120.21   $120.20   $120.20  
  7 purchase totals = $942.81       $1,021.9497   $1,021.95   $1,021.95   $1,021.90