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	$51.97	11.197%	$57.7891	$57.79	$57.80	$57.80
Purchase #2	$132.92	13.314%	$150.617	$150.62	$150.60	$150.60
Purchase #3	$76.86	11.461%	$85.6689	$85.67	$85.65	$85.70
Purchase #4	$239.61	13.566%	$272.1155	$272.12	$272.10	$272.10
Purchase #5	$120.76	9.138%	$131.795	$131.80	$131.80	$131.80
Purchase #6	$160.90	7.689%	$173.2716	$173.27	$173.25	$173.30
Purchase #7	$49.40	10.866%	$54.7678	$54.77	$54.75	$54.80
7 purchase totals =	$832.42		$926.0249	$926.04	$925.95	$926.10