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	$75.56	6.556%	$80.5137	$80.51	$80.50	$80.50
Purchase #2	$193.82	10.765%	$214.6847	$214.68	$214.70	$214.70
Purchase #3	$105.43	4.782%	$110.4717	$110.47	$110.45	$110.50
Purchase #4	$242.33	3.255%	$250.2178	$250.22	$250.20	$250.20
Purchase #5	$91.32	12.831%	$103.0373	$103.04	$103.05	$103.00
Purchase #6	$49.50	9.303%	$54.105	$54.11	$54.10	$54.10
Purchase #7	$72.39	7.230%	$77.6238	$77.62	$77.60	$77.60
7 purchase totals =	$830.35		$890.6540	$890.65	$890.60	$890.60