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	$113.54	12.274%	$127.4759	$127.48	$127.50	$127.50
Purchase #2	$88.81	6.290%	$94.3961	$94.40	$94.40	$94.40
Purchase #3	$46.56	7.577%	$50.0879	$50.09	$50.10	$50.10
Purchase #4	$150.40	10.559%	$166.2807	$166.28	$166.30	$166.30
Purchase #5	$208.79	6.834%	$223.0587	$223.06	$223.05	$223.10
Purchase #6	$130.51	11.687%	$145.7627	$145.76	$145.75	$145.80
Purchase #7	$81.55	8.462%	$88.4508	$88.45	$88.45	$88.50
7 purchase totals =	$820.16		$895.5128	$895.52	$895.55	$895.70