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	$45.32	6.236%	$48.1462	$48.15	$48.15	$48.10
Purchase #2	$161.47	9.833%	$177.3473	$177.35	$177.35	$177.30
Purchase #3	$19.92	9.870%	$21.8861	$21.89	$21.90	$21.90
Purchase #4	$129.34	4.298%	$134.899	$134.90	$134.90	$134.90
Purchase #5	$131.28	11.120%	$145.8783	$145.88	$145.90	$145.90
Purchase #6	$41.50	6.271%	$44.1025	$44.10	$44.10	$44.10
Purchase #7	$92.94	8.111%	$100.4784	$100.48	$100.50	$100.50
7 purchase totals =	$621.77		$672.7378	$672.75	$672.80	$672.70