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	$133.74	4.419%	$139.65	$139.65	$139.65	$139.70
Purchase #2	$134.34	9.342%	$146.89	$146.89	$146.90	$146.90
Purchase #3	$37.58	8.181%	$40.6544	$40.65	$40.65	$40.70
Purchase #4	$17.57	13.772%	$19.9897	$19.99	$20.00	$20.00
Purchase #5	$25.49	11.510%	$28.4239	$28.42	$28.40	$28.40
Purchase #6	$134.80	3.583%	$139.6299	$139.63	$139.65	$139.60
Purchase #7	$167.73	13.832%	$190.9304	$190.93	$190.95	$190.90
7 purchase totals =	$651.25		$706.1683	$706.16	$706.20	$706.20