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 $64.96   9.622%   $71.2105   $71.21   $71.20   $71.20  
  Purchase #2 $105.98   12.547%   $119.2773   $119.28   $119.30   $119.30  
  Purchase #3 $221.67   3.735%   $229.9494   $229.95   $229.95   $229.90  
  Purchase #4 $246.41   11.532%   $274.826   $274.83   $274.85   $274.80  
  Purchase #5 $230.69   8.761%   $250.9008   $250.90   $250.90   $250.90  
  Purchase #6 $244.54   3.409%   $252.8764   $252.88   $252.90   $252.90  
  Purchase #7 $164.35   11.695%   $183.5707   $183.57   $183.55   $183.60  
  7 purchase totals = $1,278.60       $1,382.6111   $1,382.62   $1,382.65   $1,382.60