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	$139.86	7.447%	$150.2754	$150.28	$150.30	$150.30
Purchase #2	$247.43	3.373%	$255.7758	$255.78	$255.80	$255.80
Purchase #3	$185.40	3.215%	$191.3606	$191.36	$191.35	$191.40
Purchase #4	$97.94	10.450%	$108.1747	$108.17	$108.15	$108.20
Purchase #5	$22.63	9.684%	$24.8215	$24.82	$24.80	$24.80
Purchase #6	$91.95	12.595%	$103.5311	$103.53	$103.55	$103.50
Purchase #7	$214.42	13.864%	$244.1472	$244.15	$244.15	$244.10
7 purchase totals =	$999.63		$1,078.0863	$1,078.09	$1,078.10	$1,078.10