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	$158.49	13.467%	$179.8338	$179.83	$179.85	$179.80
Purchase #2	$83.42	7.426%	$89.6148	$89.61	$89.60	$89.60
Purchase #3	$47.96	9.715%	$52.6193	$52.62	$52.60	$52.60
Purchase #4	$77.63	6.840%	$82.9399	$82.94	$82.95	$82.90
Purchase #5	$91.26	13.811%	$103.8639	$103.86	$103.85	$103.90
Purchase #6	$115.58	4.837%	$121.1706	$121.17	$121.15	$121.20
Purchase #7	$157.91	9.137%	$172.3382	$172.34	$172.35	$172.30
7 purchase totals =	$732.25		$802.3805	$802.37	$802.35	$802.30