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	$170.73	11.391%	$190.1779	$190.18	$190.20	$190.20
Purchase #2	$10.25	13.839%	$11.6685	$11.67	$11.65	$11.70
Purchase #3	$247.45	9.765%	$271.6135	$271.61	$271.60	$271.60
Purchase #4	$165.27	6.135%	$175.4093	$175.41	$175.40	$175.40
Purchase #5	$230.88	12.224%	$259.1028	$259.10	$259.10	$259.10
Purchase #6	$76.42	9.806%	$83.9137	$83.91	$83.90	$83.90
Purchase #7	$59.33	13.391%	$67.2749	$67.27	$67.25	$67.30
7 purchase totals =	$960.33		$1,059.1606	$1,059.15	$1,059.10	$1,059.20