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	$133.73	9.819%	$146.8609	$146.86	$146.85	$146.90
Purchase #2	$143.60	13.130%	$162.4547	$162.45	$162.45	$162.50
Purchase #3	$146.85	8.337%	$159.0929	$159.09	$159.10	$159.10
Purchase #4	$94.38	11.538%	$105.2696	$105.27	$105.25	$105.30
Purchase #5	$44.83	9.857%	$49.2489	$49.25	$49.25	$49.20
Purchase #6	$85.47	6.786%	$91.27	$91.27	$91.25	$91.30
Purchase #7	$106.74	3.347%	$110.3126	$110.31	$110.30	$110.30
7 purchase totals =	$755.60		$824.5096	$824.50	$824.45	$824.60