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 $224.86   8.175%   $243.2423   $243.24   $243.25   $243.20  
  Purchase #2 $45.93   3.813%   $47.6813   $47.68   $47.70   $47.70  
  Purchase #3 $149.91   12.686%   $168.9276   $168.93   $168.95   $168.90  
  Purchase #4 $172.38   7.527%   $185.355   $185.36   $185.35   $185.40  
  Purchase #5 $78.28   5.549%   $82.6238   $82.62   $82.60   $82.60  
  Purchase #6 $98.25   11.657%   $109.703   $109.70   $109.70   $109.70  
  Purchase #7 $214.65   12.840%   $242.2111   $242.21   $242.20   $242.20  
  7 purchase totals = $984.26       $1,079.7441   $1,079.74   $1,079.75   $1,079.70