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	$248.50	13.768%	$282.7135	$282.71	$282.70	$282.70
Purchase #2	$105.39	11.595%	$117.61	$117.61	$117.60	$117.60
Purchase #3	$177.43	6.246%	$188.5123	$188.51	$188.50	$188.50
Purchase #4	$93.56	6.603%	$99.7378	$99.74	$99.75	$99.70
Purchase #5	$123.76	11.770%	$138.3266	$138.33	$138.35	$138.30
Purchase #6	$127.86	10.647%	$141.4733	$141.47	$141.45	$141.50
Purchase #7	$250.86	11.490%	$279.6838	$279.68	$279.70	$279.70
7 purchase totals =	$1,127.36		$1,248.0573	$1,248.05	$1,248.05	$1,248.00