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	$40.88	4.740%	$42.8177	$42.82	$42.80	$42.80
Purchase #2	$160.52	6.397%	$170.7885	$170.79	$170.80	$170.80
Purchase #3	$129.49	9.238%	$141.4523	$141.45	$141.45	$141.50
Purchase #4	$54.61	13.406%	$61.931	$61.93	$61.95	$61.90
Purchase #5	$148.56	11.467%	$165.5954	$165.60	$165.60	$165.60
Purchase #6	$236.94	6.589%	$252.552	$252.55	$252.55	$252.60
Purchase #7	$88.93	12.585%	$100.1218	$100.12	$100.10	$100.10
7 purchase totals =	$859.93		$935.2587	$935.26	$935.25	$935.30