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	$52.51	8.707%	$57.082	$57.08	$57.10	$57.10
Purchase #2	$108.44	10.785%	$120.1353	$120.14	$120.15	$120.10
Purchase #3	$151.71	4.213%	$158.1015	$158.10	$158.10	$158.10
Purchase #4	$100.56	8.153%	$108.7587	$108.76	$108.75	$108.80
Purchase #5	$82.97	8.802%	$90.273	$90.27	$90.25	$90.30
Purchase #6	$18.51	10.623%	$20.4763	$20.48	$20.50	$20.50
Purchase #7	$173.33	9.617%	$189.9991	$190.00	$190.00	$190.00
7 purchase totals =	$688.03		$744.8259	$744.83	$744.85	$744.90