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	$15.60	6.768%	$16.6558	$16.66	$16.65	$16.70
Purchase #2	$207.61	4.180%	$216.2881	$216.29	$216.30	$216.30
Purchase #3	$11.39	4.323%	$11.8824	$11.88	$11.90	$11.90
Purchase #4	$127.61	3.262%	$131.7726	$131.77	$131.75	$131.80
Purchase #5	$90.31	9.446%	$98.8407	$98.84	$98.85	$98.80
Purchase #6	$109.32	13.253%	$123.8082	$123.81	$123.80	$123.80
Purchase #7	$60.44	10.819%	$66.979	$66.98	$67.00	$67.00
7 purchase totals =	$622.28		$666.2268	$666.23	$666.25	$666.30