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	$92.72	8.617%	$100.7097	$100.71	$100.70	$100.70
Purchase #2	$18.87	11.834%	$21.1031	$21.10	$21.10	$21.10
Purchase #3	$51.28	12.748%	$57.8172	$57.82	$57.80	$57.80
Purchase #4	$221.83	13.457%	$251.6817	$251.68	$251.70	$251.70
Purchase #5	$187.50	4.860%	$196.6125	$196.61	$196.60	$196.60
Purchase #6	$199.69	6.297%	$212.2645	$212.26	$212.25	$212.30
Purchase #7	$234.59	4.207%	$244.4592	$244.46	$244.45	$244.50
7 purchase totals =	$1,006.48		$1,084.6479	$1,084.64	$1,084.60	$1,084.70