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 $240.46   9.582%   $263.5009   $263.50   $263.50   $263.50  
  Purchase #2 $199.32   4.735%   $208.7578   $208.76   $208.75   $208.80  
  Purchase #3 $220.47   11.385%   $245.5705   $245.57   $245.55   $245.60  
  Purchase #4 $95.47   5.382%   $100.6082   $100.61   $100.60   $100.60  
  Purchase #5 $48.64   7.400%   $52.2394   $52.24   $52.25   $52.20  
  Purchase #6 $246.25   12.608%   $277.2972   $277.30   $277.30   $277.30  
  Purchase #7 $237.72   3.649%   $246.3944   $246.39   $246.40   $246.40  
  7 purchase totals = $1,288.33       $1,394.3684   $1,394.37   $1,394.35   $1,394.40