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	$27.25	10.420%	$30.0895	$30.09	$30.10	$30.10
Purchase #2	$138.38	8.566%	$150.2336	$150.23	$150.25	$150.20
Purchase #3	$187.39	4.729%	$196.2517	$196.25	$196.25	$196.30
Purchase #4	$130.75	10.194%	$144.0787	$144.08	$144.10	$144.10
Purchase #5	$14.83	4.213%	$15.4548	$15.45	$15.45	$15.50
Purchase #6	$166.38	9.590%	$182.3358	$182.34	$182.35	$182.30
Purchase #7	$239.85	3.193%	$247.5084	$247.51	$247.50	$247.50
7 purchase totals =	$904.83		$965.9525	$965.95	$966.00	$966.00