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	$90.49	11.308%	$100.7226	$100.72	$100.70	$100.70
Purchase #2	$61.91	13.359%	$70.1806	$70.18	$70.20	$70.20
Purchase #3	$58.77	6.722%	$62.7205	$62.72	$62.70	$62.70
Purchase #4	$224.38	5.627%	$237.0059	$237.01	$237.00	$237.00
Purchase #5	$27.70	7.279%	$29.7163	$29.72	$29.70	$29.70
Purchase #6	$206.56	11.603%	$230.5272	$230.53	$230.55	$230.50
Purchase #7	$59.78	7.754%	$64.4153	$64.42	$64.40	$64.40
7 purchase totals =	$729.59		$795.2884	$795.30	$795.25	$795.20