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	$179.99	4.762%	$188.5611	$188.56	$188.55	$188.60
Purchase #2	$220.61	13.321%	$249.9975	$250.00	$250.00	$250.00
Purchase #3	$64.61	12.131%	$72.4478	$72.45	$72.45	$72.40
Purchase #4	$123.30	5.143%	$129.6413	$129.64	$129.65	$129.60
Purchase #5	$72.39	7.211%	$77.61	$77.61	$77.60	$77.60
Purchase #6	$31.74	4.129%	$33.0505	$33.05	$33.05	$33.10
Purchase #7	$100.87	13.827%	$114.8173	$114.82	$114.80	$114.80
7 purchase totals =	$793.51		$866.1255	$866.13	$866.10	$866.10