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	$149.41	11.523%	$166.6265	$166.63	$166.65	$166.60
Purchase #2	$112.93	8.819%	$122.8893	$122.89	$122.90	$122.90
Purchase #3	$50.67	4.744%	$53.0738	$53.07	$53.05	$53.10
Purchase #4	$83.74	13.816%	$95.3095	$95.31	$95.30	$95.30
Purchase #5	$8.88	13.782%	$10.1038	$10.10	$10.10	$10.10
Purchase #6	$168.42	12.306%	$189.1458	$189.15	$189.15	$189.10
Purchase #7	$39.41	8.680%	$42.8308	$42.83	$42.85	$42.80
7 purchase totals =	$613.46		$679.9795	$679.98	$680.00	$679.90