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	$118.55	7.403%	$127.3263	$127.33	$127.35	$127.30
Purchase #2	$184.46	11.728%	$206.0935	$206.09	$206.10	$206.10
Purchase #3	$190.80	11.345%	$212.4463	$212.45	$212.45	$212.40
Purchase #4	$116.43	6.523%	$124.0247	$124.02	$124.00	$124.00
Purchase #5	$86.38	10.259%	$95.2417	$95.24	$95.25	$95.20
Purchase #6	$99.74	11.770%	$111.4794	$111.48	$111.50	$111.50
Purchase #7	$48.46	5.715%	$51.2295	$51.23	$51.25	$51.20
7 purchase totals =	$844.82		$927.8414	$927.84	$927.90	$927.70