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	$66.43	3.710%	$68.8946	$68.89	$68.90	$68.90
Purchase #2	$151.40	9.263%	$165.4242	$165.42	$165.40	$165.40
Purchase #3	$104.87	6.160%	$111.33	$111.33	$111.35	$111.30
Purchase #4	$207.60	4.240%	$216.4022	$216.40	$216.40	$216.40
Purchase #5	$166.87	5.188%	$175.5272	$175.53	$175.55	$175.50
Purchase #6	$59.30	9.644%	$65.0189	$65.02	$65.00	$65.00
Purchase #7	$166.94	12.729%	$188.1898	$188.19	$188.20	$188.20
7 purchase totals =	$923.41		$990.7869	$990.78	$990.80	$990.70