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	$27.82	4.589%	$29.0967	$29.10	$29.10	$29.10
Purchase #2	$106.41	7.150%	$114.0183	$114.02	$114.00	$114.00
Purchase #3	$165.94	3.843%	$172.3171	$172.32	$172.30	$172.30
Purchase #4	$20.56	4.106%	$21.4042	$21.40	$21.40	$21.40
Purchase #5	$99.75	5.762%	$105.4976	$105.50	$105.50	$105.50
Purchase #6	$176.59	3.110%	$182.0819	$182.08	$182.10	$182.10
Purchase #7	$19.57	13.171%	$22.1476	$22.15	$22.15	$22.10
7 purchase totals =	$616.64		$646.5634	$646.57	$646.55	$646.50