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	$17.86	3.186%	$18.429	$18.43	$18.45	$18.40
Purchase #2	$154.63	8.563%	$167.871	$167.87	$167.85	$167.90
Purchase #3	$21.90	7.616%	$23.5679	$23.57	$23.55	$23.60
Purchase #4	$90.70	11.759%	$101.3654	$101.37	$101.35	$101.40
Purchase #5	$230.64	10.790%	$255.5261	$255.53	$255.55	$255.50
Purchase #6	$40.61	10.515%	$44.8801	$44.88	$44.90	$44.90
Purchase #7	$18.52	12.553%	$20.8448	$20.84	$20.85	$20.80
7 purchase totals =	$574.86		$632.4843	$632.49	$632.50	$632.50