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	$238.72	5.276%	$251.3149	$251.31	$251.30	$251.30
Purchase #2	$19.84	3.419%	$20.5183	$20.52	$20.50	$20.50
Purchase #3	$143.49	12.127%	$160.891	$160.89	$160.90	$160.90
Purchase #4	$219.29	9.447%	$240.0063	$240.01	$240.00	$240.00
Purchase #5	$155.61	6.777%	$166.1557	$166.16	$166.15	$166.20
Purchase #6	$93.61	6.544%	$99.7358	$99.74	$99.75	$99.70
Purchase #7	$38.60	13.267%	$43.7211	$43.72	$43.70	$43.70
7 purchase totals =	$909.16		$982.3431	$982.35	$982.30	$982.30