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	$138.38	5.119%	$145.4637	$145.46	$145.45	$145.50
Purchase #2	$57.38	12.330%	$64.455	$64.46	$64.45	$64.50
Purchase #3	$112.36	8.205%	$121.5791	$121.58	$121.60	$121.60
Purchase #4	$121.37	4.727%	$127.1072	$127.11	$127.10	$127.10
Purchase #5	$70.95	7.582%	$76.3294	$76.33	$76.35	$76.30
Purchase #6	$43.78	10.744%	$48.4837	$48.48	$48.50	$48.50
Purchase #7	$78.52	13.626%	$89.2191	$89.22	$89.20	$89.20
7 purchase totals =	$622.74		$672.6372	$672.64	$672.65	$672.70