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 $214.61   10.348%   $236.8178   $236.82   $236.80   $236.80  
  Purchase #2 $85.74   11.482%   $95.5847   $95.58   $95.60   $95.60  
  Purchase #3 $13.29   12.253%   $14.9184   $14.92   $14.90   $14.90  
  Purchase #4 $41.99   3.758%   $43.568   $43.57   $43.55   $43.60  
  Purchase #5 $46.73   7.771%   $50.3614   $50.36   $50.35   $50.40  
  Purchase #6 $221.59   11.711%   $247.5404   $247.54   $247.55   $247.50  
  Purchase #7 $249.28   8.856%   $271.3562   $271.36   $271.35   $271.40  
  7 purchase totals = $873.23       $960.1469   $960.15   $960.10   $960.20