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	$128.42	13.269%	$145.46	$145.46	$145.45	$145.50
Purchase #2	$148.88	6.225%	$158.1478	$158.15	$158.15	$158.10
Purchase #3	$138.80	9.339%	$151.7625	$151.76	$151.75	$151.80
Purchase #4	$250.29	6.841%	$267.4123	$267.41	$267.40	$267.40
Purchase #5	$250.32	4.586%	$261.7997	$261.80	$261.80	$261.80
Purchase #6	$59.28	3.167%	$61.1574	$61.16	$61.15	$61.20
Purchase #7	$144.52	4.849%	$151.5278	$151.53	$151.55	$151.50
7 purchase totals =	$1,120.51		$1,197.2675	$1,197.27	$1,197.25	$1,197.30