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	$93.60	7.388%	$100.5152	$100.52	$100.50	$100.50
Purchase #2	$160.38	6.520%	$170.8368	$170.84	$170.85	$170.80
Purchase #3	$229.63	13.715%	$261.1238	$261.12	$261.10	$261.10
Purchase #4	$129.74	3.606%	$134.4184	$134.42	$134.40	$134.40
Purchase #5	$127.25	5.704%	$134.5083	$134.51	$134.50	$134.50
Purchase #6	$249.42	10.853%	$276.4896	$276.49	$276.50	$276.50
Purchase #7	$79.45	11.413%	$88.5176	$88.52	$88.50	$88.50
7 purchase totals =	$1,069.47		$1,166.4097	$1,166.42	$1,166.35	$1,166.30