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	$117.46	7.608%	$126.3964	$126.40	$126.40	$126.40
Purchase #2	$88.32	3.820%	$91.6938	$91.69	$91.70	$91.70
Purchase #3	$173.31	12.543%	$195.0483	$195.05	$195.05	$195.00
Purchase #4	$78.70	9.685%	$86.3221	$86.32	$86.30	$86.30
Purchase #5	$12.85	10.839%	$14.2428	$14.24	$14.25	$14.20
Purchase #6	$75.38	11.155%	$83.7886	$83.79	$83.80	$83.80
Purchase #7	$99.89	11.702%	$111.5791	$111.58	$111.60	$111.60
7 purchase totals =	$645.91		$709.0711	$709.07	$709.10	$709.00