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	$128.82	6.196%	$136.8017	$136.80	$136.80	$136.80
Purchase #2	$91.87	9.823%	$100.8944	$100.89	$100.90	$100.90
Purchase #3	$100.66	12.301%	$113.0422	$113.04	$113.05	$113.00
Purchase #4	$129.89	3.737%	$134.744	$134.74	$134.75	$134.70
Purchase #5	$72.83	5.825%	$77.0723	$77.07	$77.05	$77.10
Purchase #6	$165.52	4.808%	$173.4782	$173.48	$173.50	$173.50
Purchase #7	$90.45	6.786%	$96.5879	$96.59	$96.60	$96.60
7 purchase totals =	$780.04		$832.6207	$832.61	$832.65	$832.60