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	$199.51	5.836%	$211.1534	$211.15	$211.15	$211.20
Purchase #2	$50.38	10.216%	$55.5268	$55.53	$55.55	$55.50
Purchase #3	$240.71	13.627%	$273.5116	$273.51	$273.50	$273.50
Purchase #4	$103.26	7.598%	$111.1057	$111.11	$111.10	$111.10
Purchase #5	$17.91	10.773%	$19.8394	$19.84	$19.85	$19.80
Purchase #6	$66.36	9.171%	$72.4459	$72.45	$72.45	$72.40
Purchase #7	$135.30	11.685%	$151.1098	$151.11	$151.10	$151.10
7 purchase totals =	$813.43		$894.6926	$894.70	$894.70	$894.60