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	$23.64	3.657%	$24.5045	$24.50	$24.50	$24.50
Purchase #2	$250.89	12.853%	$283.1369	$283.14	$283.15	$283.10
Purchase #3	$106.27	10.326%	$117.2434	$117.24	$117.25	$117.20
Purchase #4	$210.72	13.620%	$239.4201	$239.42	$239.40	$239.40
Purchase #5	$140.91	13.828%	$160.395	$160.40	$160.40	$160.40
Purchase #6	$107.75	3.530%	$111.5536	$111.55	$111.55	$111.60
Purchase #7	$115.40	10.519%	$127.5389	$127.54	$127.55	$127.50
7 purchase totals =	$955.58		$1,063.7924	$1,063.79	$1,063.80	$1,063.70