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 $53.26   9.455%   $58.2957   $58.30   $58.30   $58.30  
  Purchase #2 $238.76   9.739%   $262.0128   $262.01   $262.00   $262.00  
  Purchase #3 $131.97   4.326%   $137.679   $137.68   $137.70   $137.70  
  Purchase #4 $10.71   9.383%   $11.7149   $11.71   $11.70   $11.70  
  Purchase #5 $9.43   11.432%   $10.508   $10.51   $10.50   $10.50  
  Purchase #6 $222.26   11.840%   $248.5756   $248.58   $248.60   $248.60  
  Purchase #7 $145.64   8.598%   $158.1621   $158.16   $158.15   $158.20  
  7 purchase totals = $812.03       $886.9481   $886.95   $886.95   $887.00