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	$81.64	10.363%	$90.1004	$90.10	$90.10	$90.10
Purchase #2	$13.85	11.753%	$15.4778	$15.48	$15.50	$15.50
Purchase #3	$158.90	8.729%	$172.7704	$172.77	$172.75	$172.80
Purchase #4	$196.90	10.262%	$217.1059	$217.11	$217.10	$217.10
Purchase #5	$205.43	11.296%	$228.6354	$228.64	$228.65	$228.60
Purchase #6	$171.79	10.461%	$189.761	$189.76	$189.75	$189.80
Purchase #7	$95.70	9.277%	$104.5781	$104.58	$104.60	$104.60
7 purchase totals =	$924.21		$1,018.4290	$1,018.44	$1,018.45	$1,018.50