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	$166.54	5.757%	$176.1277	$176.13	$176.15	$176.10
Purchase #2	$32.80	7.279%	$35.1875	$35.19	$35.20	$35.20
Purchase #3	$117.86	4.738%	$123.4442	$123.44	$123.45	$123.40
Purchase #4	$147.95	7.687%	$159.3229	$159.32	$159.30	$159.30
Purchase #5	$146.41	8.784%	$159.2707	$159.27	$159.25	$159.30
Purchase #6	$93.50	13.344%	$105.9766	$105.98	$106.00	$106.00
Purchase #7	$74.75	4.711%	$78.2715	$78.27	$78.25	$78.30
7 purchase totals =	$779.81		$837.6011	$837.60	$837.60	$837.60