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	$83.47	6.790%	$89.1376	$89.14	$89.15	$89.10
Purchase #2	$74.77	9.556%	$81.915	$81.92	$81.90	$81.90
Purchase #3	$156.83	10.606%	$173.4634	$173.46	$173.45	$173.50
Purchase #4	$55.47	5.532%	$58.5386	$58.54	$58.55	$58.50
Purchase #5	$20.73	10.297%	$22.8646	$22.86	$22.85	$22.90
Purchase #6	$74.78	13.409%	$84.8073	$84.81	$84.80	$84.80
Purchase #7	$173.76	6.404%	$184.8876	$184.89	$184.90	$184.90
7 purchase totals =	$639.81		$695.6141	$695.62	$695.60	$695.60