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	$210.59	6.269%	$223.7919	$223.79	$223.80	$223.80
Purchase #2	$100.96	10.792%	$111.8556	$111.86	$111.85	$111.90
Purchase #3	$147.64	5.677%	$156.0215	$156.02	$156.00	$156.00
Purchase #4	$218.87	13.137%	$247.623	$247.62	$247.60	$247.60
Purchase #5	$170.59	5.249%	$179.5443	$179.54	$179.55	$179.50
Purchase #6	$109.62	4.848%	$114.9344	$114.93	$114.95	$114.90
Purchase #7	$71.77	3.346%	$74.1714	$74.17	$74.15	$74.20
7 purchase totals =	$1,030.04		$1,107.9421	$1,107.93	$1,107.90	$1,107.90