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	$175.47	5.123%	$184.4593	$184.46	$184.45	$184.50
Purchase #2	$245.73	3.848%	$255.1857	$255.19	$255.20	$255.20
Purchase #3	$64.53	10.362%	$71.2166	$71.22	$71.20	$71.20
Purchase #4	$123.65	11.169%	$137.4605	$137.46	$137.45	$137.50
Purchase #5	$172.81	3.231%	$178.3935	$178.39	$178.40	$178.40
Purchase #6	$65.34	8.409%	$70.8344	$70.83	$70.85	$70.80
Purchase #7	$9.99	13.287%	$11.3174	$11.32	$11.30	$11.30
7 purchase totals =	$857.52		$908.8674	$908.87	$908.85	$908.90