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	$30.73	5.533%	$32.4303	$32.43	$32.45	$32.40
Purchase #2	$151.47	5.343%	$159.563	$159.56	$159.55	$159.60
Purchase #3	$140.41	8.679%	$152.5962	$152.60	$152.60	$152.60
Purchase #4	$153.88	12.374%	$172.9211	$172.92	$172.90	$172.90
Purchase #5	$32.48	13.624%	$36.9051	$36.91	$36.90	$36.90
Purchase #6	$21.99	10.368%	$24.2699	$24.27	$24.25	$24.30
Purchase #7	$245.30	12.128%	$275.05	$275.05	$275.05	$275.10
7 purchase totals =	$776.26		$853.7356	$853.74	$853.70	$853.80