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	$66.58	9.336%	$72.7959	$72.80	$72.80	$72.80
Purchase #2	$37.26	9.116%	$40.6566	$40.66	$40.65	$40.70
Purchase #3	$91.69	12.508%	$103.1586	$103.16	$103.15	$103.20
Purchase #4	$99.90	9.776%	$109.6662	$109.67	$109.65	$109.70
Purchase #5	$232.44	4.261%	$242.3443	$242.34	$242.35	$242.30
Purchase #6	$187.73	11.733%	$209.7564	$209.76	$209.75	$209.80
Purchase #7	$59.88	8.682%	$65.0788	$65.08	$65.10	$65.10
7 purchase totals =	$775.48		$843.4568	$843.47	$843.45	$843.60