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 $86.39   11.742%   $96.5339   $96.53   $96.55   $96.50  
  Purchase #2 $123.84   5.491%   $130.6401   $130.64   $130.65   $130.60  
  Purchase #3 $211.43   13.729%   $240.4572   $240.46   $240.45   $240.50  
  Purchase #4 $87.60   12.519%   $98.5666   $98.57   $98.55   $98.60  
  Purchase #5 $44.96   7.284%   $48.2349   $48.23   $48.25   $48.20  
  Purchase #6 $40.84   13.780%   $46.4678   $46.47   $46.45   $46.50  
  Purchase #7 $179.85   4.381%   $187.7292   $187.73   $187.75   $187.70  
  7 purchase totals = $774.91       $848.6297   $848.63   $848.65   $848.60