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 $217.49   3.239%   $224.5345   $224.53   $224.55   $224.50  
  Purchase #2 $203.53   5.117%   $213.9446   $213.94   $213.95   $213.90  
  Purchase #3 $173.48   5.301%   $182.6762   $182.68   $182.70   $182.70  
  Purchase #4 $22.36   4.286%   $23.3183   $23.32   $23.30   $23.30  
  Purchase #5 $160.70   5.405%   $169.3858   $169.39   $169.40   $169.40  
  Purchase #6 $7.28   12.473%   $8.188   $8.19   $8.20   $8.20  
  Purchase #7 $174.98   6.375%   $186.135   $186.14   $186.15   $186.10  
  7 purchase totals = $959.82       $1,008.1824   $1,008.19   $1,008.25   $1,008.10