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	$173.72	6.591%	$185.1699	$185.17	$185.15	$185.20
Purchase #2	$100.90	4.375%	$105.3144	$105.31	$105.30	$105.30
Purchase #3	$153.45	3.718%	$159.1553	$159.16	$159.15	$159.20
Purchase #4	$156.48	5.808%	$165.5684	$165.57	$165.55	$165.60
Purchase #5	$19.26	10.819%	$21.3437	$21.34	$21.35	$21.30
Purchase #6	$67.53	9.727%	$74.0986	$74.10	$74.10	$74.10
Purchase #7	$35.27	6.671%	$37.6229	$37.62	$37.60	$37.60
7 purchase totals =	$706.61		$748.2732	$748.27	$748.20	$748.30