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	$137.64	11.521%	$153.4975	$153.50	$153.50	$153.50
Purchase #2	$54.26	11.286%	$60.3838	$60.38	$60.40	$60.40
Purchase #3	$24.77	12.370%	$27.834	$27.83	$27.85	$27.80
Purchase #4	$57.54	4.827%	$60.3175	$60.32	$60.30	$60.30
Purchase #5	$199.39	10.777%	$220.8783	$220.88	$220.90	$220.90
Purchase #6	$131.38	9.532%	$143.9031	$143.90	$143.90	$143.90
Purchase #7	$210.90	8.653%	$229.1492	$229.15	$229.15	$229.10
7 purchase totals =	$815.88		$895.9634	$895.96	$896.00	$895.90