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	$116.50	11.517%	$129.9173	$129.92	$129.90	$129.90
Purchase #2	$83.53	7.728%	$89.9852	$89.99	$90.00	$90.00
Purchase #3	$16.89	10.490%	$18.6618	$18.66	$18.65	$18.70
Purchase #4	$25.29	8.264%	$27.38	$27.38	$27.40	$27.40
Purchase #5	$228.61	11.827%	$255.6477	$255.65	$255.65	$255.60
Purchase #6	$29.66	10.592%	$32.8016	$32.80	$32.80	$32.80
Purchase #7	$80.26	6.372%	$85.3742	$85.37	$85.35	$85.40
7 purchase totals =	$580.74		$639.7678	$639.77	$639.75	$639.80