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 $173.71   4.107%   $180.8443   $180.84   $180.85   $180.80  
  Purchase #2 $12.95   11.483%   $14.437   $14.44   $14.45   $14.40  
  Purchase #3 $90.30   12.131%   $101.2543   $101.25   $101.25   $101.30  
  Purchase #4 $20.56   8.247%   $22.2556   $22.26   $22.25   $22.30  
  Purchase #5 $148.50   6.507%   $158.1629   $158.16   $158.15   $158.20  
  Purchase #6 $66.27   7.834%   $71.4616   $71.46   $71.45   $71.50  
  Purchase #7 $141.88   12.518%   $159.6405   $159.64   $159.65   $159.60  
  7 purchase totals = $654.17       $708.0562   $708.05   $708.05   $708.10