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	$203.96	8.188%	$220.6602	$220.66	$220.65	$220.70
Purchase #2	$138.34	3.113%	$142.6465	$142.65	$142.65	$142.60
Purchase #3	$235.30	5.301%	$247.7733	$247.77	$247.75	$247.80
Purchase #4	$64.54	4.685%	$67.5637	$67.56	$67.55	$67.60
Purchase #5	$75.54	4.237%	$78.7406	$78.74	$78.75	$78.70
Purchase #6	$105.52	3.745%	$109.4717	$109.47	$109.45	$109.50
Purchase #7	$51.25	3.381%	$52.9828	$52.98	$53.00	$53.00
7 purchase totals =	$874.45		$919.8388	$919.83	$919.80	$919.90