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	$25.63	3.670%	$26.5706	$26.57	$26.55	$26.60
Purchase #2	$87.36	13.388%	$99.0558	$99.06	$99.05	$99.10
Purchase #3	$158.82	8.765%	$172.7406	$172.74	$172.75	$172.70
Purchase #4	$133.40	11.146%	$148.2688	$148.27	$148.25	$148.30
Purchase #5	$16.89	7.529%	$18.1616	$18.16	$18.15	$18.20
Purchase #6	$226.86	3.385%	$234.5392	$234.54	$234.55	$234.50
Purchase #7	$94.95	4.838%	$99.5437	$99.54	$99.55	$99.50
7 purchase totals =	$743.91		$798.8803	$798.88	$798.85	$798.90