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 $207.26   10.291%   $228.5891   $228.59   $228.60   $228.60  
  Purchase #2 $92.58   4.719%   $96.9489   $96.95   $96.95   $96.90  
  Purchase #3 $92.97   6.422%   $98.9405   $98.94   $98.95   $98.90  
  Purchase #4 $181.72   5.812%   $192.2816   $192.28   $192.30   $192.30  
  Purchase #5 $79.60   3.541%   $82.4186   $82.42   $82.40   $82.40  
  Purchase #6 $118.65   6.409%   $126.2543   $126.25   $126.25   $126.30  
  Purchase #7 $153.26   11.470%   $170.8389   $170.84   $170.85   $170.80  
  7 purchase totals = $926.04       $996.2719   $996.27   $996.30   $996.20