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	$99.54	10.301%	$109.7936	$109.79	$109.80	$109.80
Purchase #2	$147.53	13.394%	$167.2902	$167.29	$167.30	$167.30
Purchase #3	$34.39	9.549%	$37.6739	$37.67	$37.65	$37.70
Purchase #4	$158.87	10.419%	$175.4227	$175.42	$175.40	$175.40
Purchase #5	$75.47	3.613%	$78.1967	$78.20	$78.20	$78.20
Purchase #6	$40.78	3.739%	$42.3048	$42.30	$42.30	$42.30
Purchase #7	$123.69	8.336%	$134.0008	$134.00	$134.00	$134.00
7 purchase totals =	$680.27		$744.6827	$744.67	$744.65	$744.70