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 $218.35   3.523%   $226.0425   $226.04   $226.05   $226.00  
  Purchase #2 $127.97   6.655%   $136.4864   $136.49   $136.50   $136.50  
  Purchase #3 $103.58   13.249%   $117.3033   $117.30   $117.30   $117.30  
  Purchase #4 $32.98   5.294%   $34.726   $34.73   $34.75   $34.70  
  Purchase #5 $248.43   13.637%   $282.3084   $282.31   $282.30   $282.30  
  Purchase #6 $244.89   11.237%   $272.4083   $272.41   $272.40   $272.40  
  Purchase #7 $230.62   6.631%   $245.9124   $245.91   $245.90   $245.90  
  7 purchase totals = $1,206.82       $1,315.1873   $1,315.19   $1,315.20   $1,315.10