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	$21.49	4.333%	$22.4212	$22.42	$22.40	$22.40
Purchase #2	$90.82	11.417%	$101.1889	$101.19	$101.20	$101.20
Purchase #3	$105.48	11.434%	$117.5406	$117.54	$117.55	$117.50
Purchase #4	$207.30	4.505%	$216.6389	$216.64	$216.65	$216.60
Purchase #5	$114.95	11.291%	$127.929	$127.93	$127.95	$127.90
Purchase #6	$43.46	3.495%	$44.9789	$44.98	$45.00	$45.00
Purchase #7	$151.85	7.258%	$162.8713	$162.87	$162.85	$162.90
7 purchase totals =	$735.35		$793.5688	$793.57	$793.60	$793.50