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 $54.28   9.766%   $59.581   $59.58   $59.60   $59.60  
  Purchase #2 $240.47   7.241%   $257.8824   $257.88   $257.90   $257.90  
  Purchase #3 $40.96   10.559%   $45.285   $45.29   $45.30   $45.30  
  Purchase #4 $240.57   3.309%   $248.5305   $248.53   $248.55   $248.50  
  Purchase #5 $214.61   4.542%   $224.3576   $224.36   $224.35   $224.40  
  Purchase #6 $206.57   12.326%   $232.0318   $232.03   $232.05   $232.00  
  Purchase #7 $232.86   13.290%   $263.8071   $263.81   $263.80   $263.80  
  7 purchase totals = $1,230.32       $1,331.4754   $1,331.48   $1,331.55   $1,331.50