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 $237.87   10.709%   $263.3435   $263.34   $263.35   $263.30  
  Purchase #2 $13.64   12.196%   $15.3035   $15.30   $15.30   $15.30  
  Purchase #3 $248.79   5.762%   $263.1253   $263.13   $263.15   $263.10  
  Purchase #4 $162.60   5.206%   $171.065   $171.07   $171.05   $171.10  
  Purchase #5 $242.84   5.179%   $255.4167   $255.42   $255.40   $255.40  
  Purchase #6 $234.34   5.478%   $247.1771   $247.18   $247.20   $247.20  
  Purchase #7 $163.39   7.479%   $175.6099   $175.61   $175.60   $175.60  
  7 purchase totals = $1,303.47       $1,391.0410   $1,391.05   $1,391.05   $1,391.00