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	$147.91	11.575%	$165.0306	$165.03	$165.05	$165.00
Purchase #2	$112.62	4.141%	$117.2836	$117.28	$117.30	$117.30
Purchase #3	$120.86	13.749%	$137.477	$137.48	$137.50	$137.50
Purchase #4	$30.29	9.495%	$33.166	$33.17	$33.15	$33.20
Purchase #5	$105.52	12.585%	$118.7997	$118.80	$118.80	$118.80
Purchase #6	$209.29	5.817%	$221.4644	$221.46	$221.45	$221.50
Purchase #7	$137.37	6.838%	$146.7634	$146.76	$146.75	$146.80
7 purchase totals =	$863.86		$939.9847	$939.98	$940.00	$940.10