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	$11.94	4.333%	$12.4574	$12.46	$12.45	$12.50
Purchase #2	$107.94	8.127%	$116.7123	$116.71	$116.70	$116.70
Purchase #3	$50.42	7.230%	$54.0654	$54.07	$54.05	$54.10
Purchase #4	$144.41	5.203%	$151.9237	$151.92	$151.90	$151.90
Purchase #5	$88.62	7.585%	$95.3418	$95.34	$95.35	$95.30
Purchase #6	$78.73	9.174%	$85.9527	$85.95	$85.95	$86.00
Purchase #7	$53.26	8.866%	$57.982	$57.98	$58.00	$58.00
7 purchase totals =	$535.32		$574.4353	$574.43	$574.40	$574.50