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	$90.46	11.322%	$100.7019	$100.70	$100.70	$100.70
Purchase #2	$133.49	13.679%	$151.7501	$151.75	$151.75	$151.80
Purchase #3	$127.89	3.231%	$132.0221	$132.02	$132.00	$132.00
Purchase #4	$88.64	4.571%	$92.6917	$92.69	$92.70	$92.70
Purchase #5	$165.34	7.696%	$178.0646	$178.06	$178.05	$178.10
Purchase #6	$20.51	7.675%	$22.0841	$22.08	$22.10	$22.10
Purchase #7	$105.55	12.540%	$118.786	$118.79	$118.80	$118.80
7 purchase totals =	$731.88		$796.1005	$796.09	$796.10	$796.20