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	$42.30	12.334%	$47.5173	$47.52	$47.50	$47.50
Purchase #2	$59.40	9.589%	$65.0959	$65.10	$65.10	$65.10
Purchase #3	$55.32	11.433%	$61.6447	$61.64	$61.65	$61.60
Purchase #4	$149.60	13.547%	$169.8663	$169.87	$169.85	$169.90
Purchase #5	$70.82	9.539%	$77.5755	$77.58	$77.60	$77.60
Purchase #6	$153.44	11.493%	$171.0749	$171.07	$171.05	$171.10
Purchase #7	$249.30	11.696%	$278.4581	$278.46	$278.45	$278.50
7 purchase totals =	$780.18		$871.2327	$871.24	$871.20	$871.30