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 $213.47   6.464%   $227.2687   $227.27   $227.25   $227.30  
  Purchase #2 $144.91   12.763%   $163.4049   $163.40   $163.40   $163.40  
  Purchase #3 $158.58   7.666%   $170.7367   $170.74   $170.75   $170.70  
  Purchase #4 $52.70   10.573%   $58.272   $58.27   $58.25   $58.30  
  Purchase #5 $83.42   3.337%   $86.2037   $86.20   $86.20   $86.20  
  Purchase #6 $50.50   7.368%   $54.2208   $54.22   $54.20   $54.20  
  Purchase #7 $228.94   10.610%   $253.2305   $253.23   $253.25   $253.20  
  7 purchase totals = $932.52       $1,013.3373   $1,013.33   $1,013.30   $1,013.30