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 $32.89   11.273%   $36.5977   $36.60   $36.60   $36.60  
  Purchase #2 $103.58   7.563%   $111.4138   $111.41   $111.40   $111.40  
  Purchase #3 $117.87   5.284%   $124.0983   $124.10   $124.10   $124.10  
  Purchase #4 $57.79   12.239%   $64.8629   $64.86   $64.85   $64.90  
  Purchase #5 $124.44   3.756%   $129.114   $129.11   $129.10   $129.10  
  Purchase #6 $54.95   3.816%   $57.0469   $57.05   $57.05   $57.00  
  Purchase #7 $195.93   4.676%   $205.0917   $205.09   $205.10   $205.10  
  7 purchase totals = $687.45       $728.2253   $728.22   $728.20   $728.20