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 $205.42   9.203%   $224.3248   $224.32   $224.30   $224.30  
  Purchase #2 $144.59   4.698%   $151.3828   $151.38   $151.40   $151.40  
  Purchase #3 $126.34   3.462%   $130.7139   $130.71   $130.70   $130.70  
  Purchase #4 $9.95   4.823%   $10.4299   $10.43   $10.45   $10.40  
  Purchase #5 $235.61   6.309%   $250.4746   $250.47   $250.45   $250.50  
  Purchase #6 $203.37   7.491%   $218.6044   $218.60   $218.60   $218.60  
  Purchase #7 $40.49   9.457%   $44.3191   $44.32   $44.30   $44.30  
  7 purchase totals = $965.77       $1,030.2495   $1,030.23   $1,030.20   $1,030.20