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	$23.32	13.233%	$26.4059	$26.41	$26.40	$26.40
Purchase #2	$234.33	7.441%	$251.7665	$251.77	$251.75	$251.80
Purchase #3	$100.31	11.303%	$111.648	$111.65	$111.65	$111.60
Purchase #4	$217.48	8.519%	$236.0071	$236.01	$236.00	$236.00
Purchase #5	$91.53	9.623%	$100.3379	$100.34	$100.35	$100.30
Purchase #6	$220.91	6.546%	$235.3708	$235.37	$235.35	$235.40
Purchase #7	$183.77	3.613%	$190.4096	$190.41	$190.40	$190.40
7 purchase totals =	$1,071.65		$1,151.9458	$1,151.96	$1,151.90	$1,151.90