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	$154.27	7.336%	$165.5872	$165.59	$165.60	$165.60
Purchase #2	$145.49	5.806%	$153.9371	$153.94	$153.95	$153.90
Purchase #3	$149.31	8.606%	$162.1596	$162.16	$162.15	$162.20
Purchase #4	$19.73	9.303%	$21.5655	$21.57	$21.55	$21.60
Purchase #5	$95.63	6.669%	$102.0076	$102.01	$102.00	$102.00
Purchase #6	$115.25	12.826%	$130.032	$130.03	$130.05	$130.00
Purchase #7	$48.57	9.564%	$53.2152	$53.22	$53.20	$53.20
7 purchase totals =	$728.25		$788.5042	$788.52	$788.50	$788.50