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	$20.92	3.528%	$21.6581	$21.66	$21.65	$21.70
Purchase #2	$231.29	4.422%	$241.5176	$241.52	$241.50	$241.50
Purchase #3	$196.78	8.549%	$213.6027	$213.60	$213.60	$213.60
Purchase #4	$101.54	8.838%	$110.5141	$110.51	$110.50	$110.50
Purchase #5	$98.89	11.108%	$109.8747	$109.87	$109.85	$109.90
Purchase #6	$231.46	9.374%	$253.1571	$253.16	$253.15	$253.20
Purchase #7	$65.58	3.570%	$67.9212	$67.92	$67.90	$67.90
7 purchase totals =	$946.46		$1,018.2455	$1,018.24	$1,018.15	$1,018.30