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	$17.76	5.183%	$18.6805	$18.68	$18.70	$18.70
Purchase #2	$210.27	9.675%	$230.6136	$230.61	$230.60	$230.60
Purchase #3	$83.49	6.533%	$88.9444	$88.94	$88.95	$88.90
Purchase #4	$92.46	7.572%	$99.4611	$99.46	$99.45	$99.50
Purchase #5	$36.63	6.203%	$38.9022	$38.90	$38.90	$38.90
Purchase #6	$48.35	11.110%	$53.7217	$53.72	$53.70	$53.70
Purchase #7	$9.34	12.717%	$10.5278	$10.53	$10.55	$10.50
7 purchase totals =	$498.30		$540.8513	$540.84	$540.85	$540.80