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	$171.85	9.552%	$188.2651	$188.27	$188.25	$188.30
Purchase #2	$149.95	10.558%	$165.7817	$165.78	$165.80	$165.80
Purchase #3	$114.59	7.773%	$123.4971	$123.50	$123.50	$123.50
Purchase #4	$83.43	4.367%	$87.0734	$87.07	$87.05	$87.10
Purchase #5	$246.91	3.391%	$255.2827	$255.28	$255.30	$255.30
Purchase #6	$91.32	9.848%	$100.3132	$100.31	$100.30	$100.30
Purchase #7	$33.29	12.431%	$37.4283	$37.43	$37.45	$37.40
7 purchase totals =	$891.34		$957.6415	$957.64	$957.65	$957.70