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 $240.33   7.749%   $258.9532   $258.95   $258.95   $259.00  
  Purchase #2 $118.43   12.868%   $133.6696   $133.67   $133.65   $133.70  
  Purchase #3 $243.41   7.437%   $261.5124   $261.51   $261.50   $261.50  
  Purchase #4 $7.85   11.802%   $8.7765   $8.78   $8.80   $8.80  
  Purchase #5 $151.76   12.136%   $170.1776   $170.18   $170.20   $170.20  
  Purchase #6 $8.77   5.478%   $9.2504   $9.25   $9.25   $9.30  
  Purchase #7 $204.94   7.670%   $220.6589   $220.66   $220.65   $220.70  
  7 purchase totals = $975.49       $1,062.9986   $1,063.00   $1,063.00   $1,063.20