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	$50.39	10.658%	$55.7606	$55.76	$55.75	$55.80
Purchase #2	$188.48	5.155%	$198.1961	$198.20	$198.20	$198.20
Purchase #3	$180.72	10.338%	$199.4028	$199.40	$199.40	$199.40
Purchase #4	$144.48	4.755%	$151.35	$151.35	$151.35	$151.40
Purchase #5	$230.72	8.390%	$250.0774	$250.08	$250.10	$250.10
Purchase #6	$18.56	11.156%	$20.6306	$20.63	$20.65	$20.60
Purchase #7	$30.88	8.144%	$33.3949	$33.39	$33.40	$33.40
7 purchase totals =	$844.23		$908.8124	$908.81	$908.85	$908.90