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	$75.83	4.663%	$79.366	$79.37	$79.35	$79.40
Purchase #2	$182.83	3.849%	$189.8671	$189.87	$189.85	$189.90
Purchase #3	$109.77	5.799%	$116.1356	$116.14	$116.15	$116.10
Purchase #4	$179.58	13.283%	$203.4336	$203.43	$203.45	$203.40
Purchase #5	$141.48	12.262%	$158.8283	$158.83	$158.85	$158.80
Purchase #6	$230.69	8.538%	$250.3863	$250.39	$250.40	$250.40
Purchase #7	$97.83	5.266%	$102.9817	$102.98	$103.00	$103.00
7 purchase totals =	$1,018.01		$1,100.9986	$1,101.01	$1,101.05	$1,101.00