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	$134.28	6.614%	$143.1613	$143.16	$143.15	$143.20
Purchase #2	$59.89	8.718%	$65.1112	$65.11	$65.10	$65.10
Purchase #3	$90.29	4.769%	$94.5959	$94.60	$94.60	$94.60
Purchase #4	$85.85	6.271%	$91.2337	$91.23	$91.25	$91.20
Purchase #5	$149.90	11.139%	$166.5974	$166.60	$166.60	$166.60
Purchase #6	$63.37	4.382%	$66.1469	$66.15	$66.15	$66.10
Purchase #7	$158.70	4.587%	$165.9796	$165.98	$166.00	$166.00
7 purchase totals =	$742.28		$792.8260	$792.83	$792.85	$792.80