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	$90.84	8.538%	$98.5959	$98.60	$98.60	$98.60
Purchase #2	$133.58	4.657%	$139.8008	$139.80	$139.80	$139.80
Purchase #3	$158.43	5.650%	$167.3813	$167.38	$167.40	$167.40
Purchase #4	$218.30	7.751%	$235.2204	$235.22	$235.20	$235.20
Purchase #5	$10.48	10.777%	$11.6094	$11.61	$11.60	$11.60
Purchase #6	$28.70	9.150%	$31.3261	$31.33	$31.35	$31.30
Purchase #7	$38.52	4.688%	$40.3258	$40.33	$40.35	$40.30
7 purchase totals =	$678.85		$724.2597	$724.27	$724.30	$724.20