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	$66.54	7.418%	$71.4759	$71.48	$71.50	$71.50
Purchase #2	$208.59	10.728%	$230.9675	$230.97	$230.95	$231.00
Purchase #3	$109.34	8.277%	$118.3901	$118.39	$118.40	$118.40
Purchase #4	$10.92	13.443%	$12.388	$12.39	$12.40	$12.40
Purchase #5	$17.37	8.571%	$18.8588	$18.86	$18.85	$18.90
Purchase #6	$96.35	5.565%	$101.7119	$101.71	$101.70	$101.70
Purchase #7	$50.48	4.689%	$52.847	$52.85	$52.85	$52.80
7 purchase totals =	$559.59		$606.6392	$606.65	$606.65	$606.70