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	$233.45	10.698%	$258.4245	$258.42	$258.40	$258.40
Purchase #2	$146.40	4.433%	$152.8899	$152.89	$152.90	$152.90
Purchase #3	$152.75	12.163%	$171.329	$171.33	$171.35	$171.30
Purchase #4	$130.74	9.681%	$143.3969	$143.40	$143.40	$143.40
Purchase #5	$18.78	13.427%	$21.3016	$21.30	$21.30	$21.30
Purchase #6	$159.57	7.109%	$170.9138	$170.91	$170.90	$170.90
Purchase #7	$112.75	12.668%	$127.0332	$127.03	$127.05	$127.00
7 purchase totals =	$954.44		$1,045.2889	$1,045.28	$1,045.30	$1,045.20