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	$220.73	9.453%	$241.5956	$241.60	$241.60	$241.60
Purchase #2	$140.58	6.777%	$150.1071	$150.11	$150.10	$150.10
Purchase #3	$133.53	9.267%	$145.9042	$145.90	$145.90	$145.90
Purchase #4	$112.42	5.479%	$118.5795	$118.58	$118.60	$118.60
Purchase #5	$215.41	12.225%	$241.7439	$241.74	$241.75	$241.70
Purchase #6	$25.90	10.493%	$28.6177	$28.62	$28.60	$28.60
Purchase #7	$141.98	11.805%	$158.7407	$158.74	$158.75	$158.70
7 purchase totals =	$990.55		$1,085.2887	$1,085.29	$1,085.30	$1,085.20