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	$230.82	6.281%	$245.3178	$245.32	$245.30	$245.30
Purchase #2	$200.42	13.838%	$228.1541	$228.15	$228.15	$228.20
Purchase #3	$106.44	13.191%	$120.4805	$120.48	$120.50	$120.50
Purchase #4	$46.68	6.451%	$49.6913	$49.69	$49.70	$49.70
Purchase #5	$129.28	9.710%	$141.8331	$141.83	$141.85	$141.80
Purchase #6	$151.83	10.589%	$167.9073	$167.91	$167.90	$167.90
Purchase #7	$55.88	7.153%	$59.8771	$59.88	$59.90	$59.90
7 purchase totals =	$921.35		$1,013.2612	$1,013.26	$1,013.30	$1,013.30