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	$151.30	12.597%	$170.3593	$170.36	$170.35	$170.40
Purchase #2	$118.61	12.632%	$133.5928	$133.59	$133.60	$133.60
Purchase #3	$236.53	4.457%	$247.0721	$247.07	$247.05	$247.10
Purchase #4	$33.54	13.371%	$38.0246	$38.02	$38.00	$38.00
Purchase #5	$99.98	3.597%	$103.5763	$103.58	$103.60	$103.60
Purchase #6	$51.91	9.219%	$56.6956	$56.70	$56.70	$56.70
Purchase #7	$105.35	5.489%	$111.1327	$111.13	$111.15	$111.10
7 purchase totals =	$797.22		$860.4534	$860.45	$860.45	$860.50