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 $242.27   11.142%   $269.2637   $269.26   $269.25   $269.30  
  Purchase #2 $125.77   10.462%   $138.9281   $138.93   $138.95   $138.90  
  Purchase #3 $220.35   7.381%   $236.614   $236.61   $236.60   $236.60  
  Purchase #4 $80.98   6.171%   $85.9773   $85.98   $86.00   $86.00  
  Purchase #5 $215.38   6.421%   $229.2095   $229.21   $229.20   $229.20  
  Purchase #6 $237.85   5.675%   $251.348   $251.35   $251.35   $251.30  
  Purchase #7 $61.41   5.184%   $64.5935   $64.59   $64.60   $64.60  
  7 purchase totals = $1,184.01       $1,275.9341   $1,275.93   $1,275.95   $1,275.90