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	$52.35	3.523%	$54.1943	$54.19	$54.20	$54.20
Purchase #2	$98.92	12.318%	$111.105	$111.11	$111.10	$111.10
Purchase #3	$249.95	6.388%	$265.9168	$265.92	$265.90	$265.90
Purchase #4	$11.96	5.806%	$12.6544	$12.65	$12.65	$12.70
Purchase #5	$161.34	13.255%	$182.7256	$182.73	$182.75	$182.70
Purchase #6	$205.86	8.482%	$223.321	$223.32	$223.30	$223.30
Purchase #7	$90.48	10.695%	$100.1568	$100.16	$100.15	$100.20
7 purchase totals =	$870.86		$950.0739	$950.08	$950.05	$950.10