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 $104.89   9.250%   $114.5923   $114.59   $114.60   $114.60  
  Purchase #2 $240.69   6.428%   $256.1616   $256.16   $256.15   $256.20  
  Purchase #3 $22.47   8.335%   $24.3429   $24.34   $24.35   $24.30  
  Purchase #4 $231.41   10.344%   $255.3471   $255.35   $255.35   $255.30  
  Purchase #5 $123.67   8.426%   $134.0904   $134.09   $134.10   $134.10  
  Purchase #6 $177.74   9.544%   $194.7035   $194.70   $194.70   $194.70  
  Purchase #7 $32.49   5.304%   $34.2133   $34.21   $34.20   $34.20  
  7 purchase totals = $933.36       $1,013.4511   $1,013.44   $1,013.45   $1,013.40