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	$138.28	6.174%	$146.8174	$146.82	$146.80	$146.80
Purchase #2	$212.92	7.848%	$229.63	$229.63	$229.65	$229.60
Purchase #3	$32.49	12.624%	$36.5915	$36.59	$36.60	$36.60
Purchase #4	$47.78	13.468%	$54.215	$54.22	$54.20	$54.20
Purchase #5	$166.25	13.559%	$188.7918	$188.79	$188.80	$188.80
Purchase #6	$170.29	12.107%	$190.907	$190.91	$190.90	$190.90
Purchase #7	$215.56	7.360%	$231.4252	$231.43	$231.45	$231.40
7 purchase totals =	$983.57		$1,078.3779	$1,078.39	$1,078.40	$1,078.30