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	$74.97	11.784%	$83.8045	$83.80	$83.80	$83.80
Purchase #2	$8.58	12.282%	$9.6338	$9.63	$9.65	$9.60
Purchase #3	$51.25	5.128%	$53.8781	$53.88	$53.90	$53.90
Purchase #4	$100.66	11.841%	$112.5792	$112.58	$112.60	$112.60
Purchase #5	$90.91	13.733%	$103.3947	$103.39	$103.40	$103.40
Purchase #6	$204.84	8.510%	$222.2719	$222.27	$222.25	$222.30
Purchase #7	$11.89	6.498%	$12.6626	$12.66	$12.65	$12.70
7 purchase totals =	$543.10		$598.2248	$598.21	$598.25	$598.30