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	$20.72	13.858%	$23.5914	$23.59	$23.60	$23.60
Purchase #2	$152.36	5.620%	$160.9226	$160.92	$160.90	$160.90
Purchase #3	$146.41	12.137%	$164.1798	$164.18	$164.20	$164.20
Purchase #4	$56.94	8.195%	$61.6062	$61.61	$61.60	$61.60
Purchase #5	$196.49	12.173%	$220.4087	$220.41	$220.40	$220.40
Purchase #6	$228.92	6.493%	$243.7838	$243.78	$243.80	$243.80
Purchase #7	$173.73	9.746%	$190.6617	$190.66	$190.65	$190.70
7 purchase totals =	$975.57		$1,065.1542	$1,065.15	$1,065.15	$1,065.20