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	$173.88	8.204%	$188.1451	$188.15	$188.15	$188.10
Purchase #2	$58.34	5.370%	$61.4729	$61.47	$61.45	$61.50
Purchase #3	$174.84	9.142%	$190.8239	$190.82	$190.80	$190.80
Purchase #4	$98.81	7.750%	$106.4678	$106.47	$106.45	$106.50
Purchase #5	$48.37	4.277%	$50.4388	$50.44	$50.45	$50.40
Purchase #6	$33.34	11.188%	$37.0701	$37.07	$37.05	$37.10
Purchase #7	$72.41	3.771%	$75.1406	$75.14	$75.15	$75.10
7 purchase totals =	$659.99		$709.5592	$709.56	$709.50	$709.50