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	$102.89	8.241%	$111.3692	$111.37	$111.35	$111.40
Purchase #2	$90.44	10.142%	$99.6124	$99.61	$99.60	$99.60
Purchase #3	$105.50	12.589%	$118.7814	$118.78	$118.80	$118.80
Purchase #4	$127.62	11.410%	$142.1814	$142.18	$142.20	$142.20
Purchase #5	$239.83	4.298%	$250.1379	$250.14	$250.15	$250.10
Purchase #6	$174.99	11.216%	$194.6169	$194.62	$194.60	$194.60
Purchase #7	$39.32	5.399%	$41.4429	$41.44	$41.45	$41.40
7 purchase totals =	$880.59		$958.1421	$958.14	$958.15	$958.10