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 $103.77   7.868%   $111.9346   $111.93   $111.95   $111.90  
  Purchase #2 $159.39   10.222%   $175.6828   $175.68   $175.70   $175.70  
  Purchase #3 $80.78   12.762%   $91.0891   $91.09   $91.10   $91.10  
  Purchase #4 $240.38   9.466%   $263.1344   $263.13   $263.15   $263.10  
  Purchase #5 $250.97   3.491%   $259.7314   $259.73   $259.75   $259.70  
  Purchase #6 $48.41   4.692%   $50.6814   $50.68   $50.70   $50.70  
  Purchase #7 $59.66   3.387%   $61.6807   $61.68   $61.70   $61.70  
  7 purchase totals = $943.36       $1,013.9344   $1,013.92   $1,014.05   $1,013.90