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	$25.25	5.436%	$26.6226	$26.62	$26.60	$26.60
Purchase #2	$232.58	12.792%	$262.3316	$262.33	$262.35	$262.30
Purchase #3	$203.48	8.229%	$220.2244	$220.22	$220.20	$220.20
Purchase #4	$99.25	4.241%	$103.4592	$103.46	$103.45	$103.50
Purchase #5	$145.59	11.782%	$162.7434	$162.74	$162.75	$162.70
Purchase #6	$30.63	10.419%	$33.8213	$33.82	$33.80	$33.80
Purchase #7	$107.38	3.490%	$111.1276	$111.13	$111.15	$111.10
7 purchase totals =	$844.16		$920.3301	$920.32	$920.30	$920.20