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	$212.73	13.103%	$240.604	$240.60	$240.60	$240.60
Purchase #2	$224.55	11.527%	$250.4339	$250.43	$250.45	$250.40
Purchase #3	$99.64	5.853%	$105.4719	$105.47	$105.45	$105.50
Purchase #4	$77.26	10.425%	$85.3144	$85.31	$85.30	$85.30
Purchase #5	$207.36	12.642%	$233.5745	$233.57	$233.55	$233.60
Purchase #6	$190.51	4.128%	$198.3743	$198.37	$198.35	$198.40
Purchase #7	$139.52	10.802%	$154.591	$154.59	$154.60	$154.60
7 purchase totals =	$1,151.57		$1,268.3640	$1,268.34	$1,268.30	$1,268.40