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	$19.74	5.667%	$20.8587	$20.86	$20.85	$20.90
Purchase #2	$120.50	8.567%	$130.8232	$130.82	$130.80	$130.80
Purchase #3	$60.32	7.387%	$64.7758	$64.78	$64.80	$64.80
Purchase #4	$178.66	9.772%	$196.1187	$196.12	$196.10	$196.10
Purchase #5	$32.64	12.828%	$36.8271	$36.83	$36.85	$36.80
Purchase #6	$88.30	6.182%	$93.7587	$93.76	$93.75	$93.80
Purchase #7	$91.88	13.730%	$104.4951	$104.50	$104.50	$104.50
7 purchase totals =	$592.04		$647.6573	$647.67	$647.65	$647.70