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	$96.76	10.147%	$106.5782	$106.58	$106.60	$106.60
Purchase #2	$203.64	11.736%	$227.5392	$227.54	$227.55	$227.50
Purchase #3	$123.62	10.733%	$136.8881	$136.89	$136.90	$136.90
Purchase #4	$153.71	3.497%	$159.0852	$159.09	$159.10	$159.10
Purchase #5	$216.54	5.271%	$227.9538	$227.95	$227.95	$228.00
Purchase #6	$161.38	7.152%	$172.9219	$172.92	$172.90	$172.90
Purchase #7	$62.47	11.127%	$69.421	$69.42	$69.40	$69.40
7 purchase totals =	$1,018.12		$1,100.3874	$1,100.39	$1,100.40	$1,100.40