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 $216.54   13.726%   $246.2623   $246.26   $246.25   $246.30  
  Purchase #2 $209.78   11.306%   $233.4977   $233.50   $233.50   $233.50  
  Purchase #3 $177.44   8.331%   $192.2225   $192.22   $192.20   $192.20  
  Purchase #4 $223.70   8.714%   $243.1932   $243.19   $243.20   $243.20  
  Purchase #5 $23.66   5.867%   $25.0481   $25.05   $25.05   $25.00  
  Purchase #6 $21.39   8.122%   $23.1273   $23.13   $23.15   $23.10  
  Purchase #7 $98.54   13.582%   $111.9237   $111.92   $111.90   $111.90  
  7 purchase totals = $971.05       $1,075.2748   $1,075.27   $1,075.25   $1,075.20