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 $239.91   8.834%   $261.1036   $261.10   $261.10   $261.10  
  Purchase #2 $175.42   5.813%   $185.6172   $185.62   $185.60   $185.60  
  Purchase #3 $135.29   8.815%   $147.2158   $147.22   $147.20   $147.20  
  Purchase #4 $217.54   7.690%   $234.2688   $234.27   $234.25   $234.30  
  Purchase #5 $77.88   5.621%   $82.2576   $82.26   $82.25   $82.30  
  Purchase #6 $146.57   7.324%   $157.3048   $157.30   $157.30   $157.30  
  Purchase #7 $182.53   8.274%   $197.6325   $197.63   $197.65   $197.60  
  7 purchase totals = $1,175.14       $1,265.4003   $1,265.40   $1,265.35   $1,265.40