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	$124.62	9.406%	$136.3418	$136.34	$136.35	$136.30
Purchase #2	$244.91	12.338%	$275.127	$275.13	$275.15	$275.10
Purchase #3	$106.38	13.445%	$120.6828	$120.68	$120.70	$120.70
Purchase #4	$133.89	8.496%	$145.2653	$145.27	$145.25	$145.30
Purchase #5	$59.49	10.401%	$65.6776	$65.68	$65.70	$65.70
Purchase #6	$83.61	7.212%	$89.64	$89.64	$89.65	$89.60
Purchase #7	$235.93	12.599%	$265.6548	$265.65	$265.65	$265.70
7 purchase totals =	$988.83		$1,098.3893	$1,098.39	$1,098.45	$1,098.40