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	$247.83	7.165%	$265.587	$265.59	$265.60	$265.60
Purchase #2	$37.87	11.229%	$42.1224	$42.12	$42.10	$42.10
Purchase #3	$87.78	11.737%	$98.0827	$98.08	$98.10	$98.10
Purchase #4	$161.72	13.676%	$183.8368	$183.84	$183.85	$183.80
Purchase #5	$114.65	11.859%	$128.2463	$128.25	$128.25	$128.20
Purchase #6	$16.64	10.113%	$18.3228	$18.32	$18.30	$18.30
Purchase #7	$11.74	6.313%	$12.4811	$12.48	$12.50	$12.50
7 purchase totals =	$678.23		$748.6791	$748.68	$748.70	$748.60