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	$96.98	12.674%	$109.2712	$109.27	$109.25	$109.30
Purchase #2	$105.59	6.759%	$112.7268	$112.73	$112.75	$112.70
Purchase #3	$150.91	3.379%	$156.0092	$156.01	$156.00	$156.00
Purchase #4	$37.94	10.103%	$41.7731	$41.77	$41.75	$41.80
Purchase #5	$92.56	8.265%	$100.2101	$100.21	$100.20	$100.20
Purchase #6	$145.68	12.471%	$163.8478	$163.85	$163.85	$163.80
Purchase #7	$105.92	4.853%	$111.0603	$111.06	$111.05	$111.10
7 purchase totals =	$735.58		$794.8985	$794.90	$794.85	$794.90