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 $227.83   13.400%   $258.3592   $258.36   $258.35   $258.40  
  Purchase #2 $57.95   4.858%   $60.7652   $60.77   $60.75   $60.80  
  Purchase #3 $182.82   6.722%   $195.1092   $195.11   $195.10   $195.10  
  Purchase #4 $34.43   3.250%   $35.549   $35.55   $35.55   $35.50  
  Purchase #5 $118.44   6.831%   $126.5306   $126.53   $126.55   $126.50  
  Purchase #6 $231.74   12.842%   $261.5001   $261.50   $261.50   $261.50  
  Purchase #7 $231.94   7.206%   $248.6536   $248.65   $248.65   $248.70  
  7 purchase totals = $1,085.15       $1,186.4669   $1,186.47   $1,186.45   $1,186.50