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	$18.30	3.197%	$18.8851	$18.89	$18.90	$18.90
Purchase #2	$7.62	4.475%	$7.961	$7.96	$7.95	$8.00
Purchase #3	$118.46	8.607%	$128.6559	$128.66	$128.65	$128.70
Purchase #4	$132.77	6.295%	$141.1279	$141.13	$141.15	$141.10
Purchase #5	$52.48	10.229%	$57.8482	$57.85	$57.85	$57.80
Purchase #6	$90.94	10.170%	$100.1886	$100.19	$100.20	$100.20
Purchase #7	$140.40	3.467%	$145.2677	$145.27	$145.25	$145.30
7 purchase totals =	$560.97		$599.9344	$599.95	$599.95	$600.00