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 $106.65   6.377%   $113.4511   $113.45   $113.45   $113.50  
  Purchase #2 $208.95   4.175%   $217.6737   $217.67   $217.65   $217.70  
  Purchase #3 $147.59   5.204%   $155.2706   $155.27   $155.25   $155.30  
  Purchase #4 $40.93   4.324%   $42.6998   $42.70   $42.70   $42.70  
  Purchase #5 $79.71   9.400%   $87.2027   $87.20   $87.20   $87.20  
  Purchase #6 $222.38   6.872%   $237.662   $237.66   $237.65   $237.70  
  Purchase #7 $218.27   6.834%   $233.1866   $233.19   $233.20   $233.20  
  7 purchase totals = $1,024.48       $1,087.1465   $1,087.14   $1,087.10   $1,087.30