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 $213.43   9.757%   $234.2544   $234.25   $234.25   $234.30  
  Purchase #2 $208.88   12.448%   $234.8814   $234.88   $234.90   $234.90  
  Purchase #3 $125.83   12.672%   $141.7752   $141.78   $141.80   $141.80  
  Purchase #4 $240.54   12.690%   $271.0645   $271.06   $271.05   $271.10  
  Purchase #5 $245.27   5.600%   $259.0051   $259.01   $259.00   $259.00  
  Purchase #6 $92.35   3.541%   $95.6201   $95.62   $95.60   $95.60  
  Purchase #7 $89.40   3.621%   $92.6372   $92.64   $92.65   $92.60  
  7 purchase totals = $1,215.70       $1,329.2379   $1,329.24   $1,329.25   $1,329.30