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	$150.79	5.403%	$158.9372	$158.94	$158.95	$158.90
Purchase #2	$53.97	9.554%	$59.1263	$59.13	$59.15	$59.10
Purchase #3	$48.37	12.587%	$54.4583	$54.46	$54.45	$54.50
Purchase #4	$149.73	6.603%	$159.6167	$159.62	$159.60	$159.60
Purchase #5	$163.88	8.864%	$178.4063	$178.41	$178.40	$178.40
Purchase #6	$164.28	5.208%	$172.8357	$172.84	$172.85	$172.80
Purchase #7	$93.84	6.643%	$100.0738	$100.07	$100.05	$100.10
7 purchase totals =	$824.86		$883.4543	$883.47	$883.45	$883.40