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	$20.92	9.547%	$22.9172	$22.92	$22.90	$22.90
Purchase #2	$116.52	6.873%	$124.5284	$124.53	$124.55	$124.50
Purchase #3	$85.46	3.578%	$88.5178	$88.52	$88.50	$88.50
Purchase #4	$240.74	3.677%	$249.592	$249.59	$249.60	$249.60
Purchase #5	$24.62	3.332%	$25.4403	$25.44	$25.45	$25.40
Purchase #6	$100.90	10.116%	$111.107	$111.11	$111.10	$111.10
Purchase #7	$53.97	8.222%	$58.4074	$58.41	$58.40	$58.40
7 purchase totals =	$643.13		$680.5101	$680.52	$680.50	$680.40