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 $232.37   12.807%   $262.1296   $262.13   $262.15   $262.10  
  Purchase #2 $116.89   7.755%   $125.9548   $125.95   $125.95   $126.00  
  Purchase #3 $50.67   4.742%   $53.0728   $53.07   $53.05   $53.10  
  Purchase #4 $177.97   7.253%   $190.8782   $190.88   $190.90   $190.90  
  Purchase #5 $6.30   12.707%   $7.1005   $7.10   $7.10   $7.10  
  Purchase #6 $103.60   13.872%   $117.9714   $117.97   $117.95   $118.00  
  Purchase #7 $241.25   5.456%   $254.4126   $254.41   $254.40   $254.40  
  7 purchase totals = $929.05       $1,011.5199   $1,011.51   $1,011.50   $1,011.60