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	$200.54	4.104%	$208.7702	$208.77	$208.75	$208.80
Purchase #2	$239.72	13.102%	$271.1281	$271.13	$271.15	$271.10
Purchase #3	$23.56	4.432%	$24.6042	$24.60	$24.60	$24.60
Purchase #4	$233.83	9.408%	$255.8287	$255.83	$255.85	$255.80
Purchase #5	$224.73	10.385%	$248.0682	$248.07	$248.05	$248.10
Purchase #6	$128.55	12.520%	$144.6445	$144.64	$144.65	$144.60
Purchase #7	$178.77	5.851%	$189.2298	$189.23	$189.25	$189.20
7 purchase totals =	$1,229.70		$1,342.2737	$1,342.27	$1,342.30	$1,342.20