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 $192.65   11.216%   $214.2576   $214.26   $214.25   $214.30  
  Purchase #2 $67.83   5.463%   $71.5356   $71.54   $71.55   $71.50  
  Purchase #3 $41.60   13.146%   $47.0687   $47.07   $47.05   $47.10  
  Purchase #4 $39.40   4.563%   $41.1978   $41.20   $41.20   $41.20  
  Purchase #5 $179.27   3.213%   $185.0299   $185.03   $185.05   $185.00  
  Purchase #6 $230.83   10.339%   $254.6955   $254.70   $254.70   $254.70  
  Purchase #7 $136.94   6.164%   $145.381   $145.38   $145.40   $145.40  
  7 purchase totals = $888.52       $959.1661   $959.18   $959.20   $959.20