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	$36.64	4.736%	$38.3753	$38.38	$38.40	$38.40
Purchase #2	$50.42	10.775%	$55.8528	$55.85	$55.85	$55.90
Purchase #3	$218.53	12.767%	$246.4297	$246.43	$246.45	$246.40
Purchase #4	$238.84	13.834%	$271.8811	$271.88	$271.90	$271.90
Purchase #5	$109.38	5.174%	$115.0393	$115.04	$115.05	$115.00
Purchase #6	$230.69	8.437%	$250.1533	$250.15	$250.15	$250.20
Purchase #7	$129.37	12.463%	$145.4934	$145.49	$145.50	$145.50
7 purchase totals =	$1,013.87		$1,123.2249	$1,123.22	$1,123.30	$1,123.30