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	$74.74	5.666%	$78.9748	$78.97	$78.95	$79.00
Purchase #2	$85.72	5.569%	$90.4937	$90.49	$90.50	$90.50
Purchase #3	$239.51	4.481%	$250.2424	$250.24	$250.25	$250.20
Purchase #4	$55.63	10.141%	$61.2714	$61.27	$61.25	$61.30
Purchase #5	$106.28	3.707%	$110.2198	$110.22	$110.20	$110.20
Purchase #6	$112.75	8.538%	$122.3766	$122.38	$122.40	$122.40
Purchase #7	$14.89	4.240%	$15.5213	$15.52	$15.50	$15.50
7 purchase totals =	$689.52		$729.1000	$729.09	$729.05	$729.10