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 $224.25   9.683%   $245.9641   $245.96   $245.95   $246.00  
  Purchase #2 $180.41   7.394%   $193.7495   $193.75   $193.75   $193.70  
  Purchase #3 $154.26   3.325%   $159.3891   $159.39   $159.40   $159.40  
  Purchase #4 $225.54   6.541%   $240.2926   $240.29   $240.30   $240.30  
  Purchase #5 $50.63   4.516%   $52.9165   $52.92   $52.90   $52.90  
  Purchase #6 $233.39   10.523%   $257.9496   $257.95   $257.95   $257.90  
  Purchase #7 $42.86   12.759%   $48.3285   $48.33   $48.35   $48.30  
  7 purchase totals = $1,111.34       $1,198.5899   $1,198.59   $1,198.60   $1,198.50