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	$191.72	12.796%	$216.2525	$216.25	$216.25	$216.30
Purchase #2	$246.35	10.622%	$272.5173	$272.52	$272.50	$272.50
Purchase #3	$195.43	5.444%	$206.0692	$206.07	$206.05	$206.10
Purchase #4	$50.31	7.582%	$54.1245	$54.12	$54.10	$54.10
Purchase #5	$215.78	3.711%	$223.7876	$223.79	$223.80	$223.80
Purchase #6	$156.97	10.180%	$172.9495	$172.95	$172.95	$172.90
Purchase #7	$152.97	3.827%	$158.8242	$158.82	$158.80	$158.80
7 purchase totals =	$1,209.53		$1,304.5248	$1,304.52	$1,304.45	$1,304.50