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 $208.61   13.526%   $236.8266   $236.83   $236.85   $236.80  
  Purchase #2 $161.63   12.599%   $181.9938   $181.99   $182.00   $182.00  
  Purchase #3 $240.56   3.693%   $249.4439   $249.44   $249.45   $249.40  
  Purchase #4 $181.82   7.318%   $195.1256   $195.13   $195.15   $195.10  
  Purchase #5 $22.93   7.278%   $24.5988   $24.60   $24.60   $24.60  
  Purchase #6 $23.74   3.619%   $24.5992   $24.60   $24.60   $24.60  
  Purchase #7 $99.30   13.503%   $112.7085   $112.71   $112.70   $112.70  
  7 purchase totals = $938.59       $1,025.2964   $1,025.30   $1,025.35   $1,025.20