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	$228.33	12.173%	$256.1246	$256.12	$256.10	$256.10
Purchase #2	$189.49	3.362%	$195.8607	$195.86	$195.85	$195.90
Purchase #3	$135.50	13.156%	$153.3264	$153.33	$153.35	$153.30
Purchase #4	$98.97	6.556%	$105.4585	$105.46	$105.45	$105.50
Purchase #5	$32.93	8.197%	$35.6293	$35.63	$35.65	$35.60
Purchase #6	$97.89	12.621%	$110.2447	$110.24	$110.25	$110.20
Purchase #7	$83.50	13.203%	$94.5245	$94.52	$94.50	$94.50
7 purchase totals =	$866.61		$951.1687	$951.16	$951.15	$951.10