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	$220.79	5.823%	$233.6466	$233.65	$233.65	$233.60
Purchase #2	$42.43	8.542%	$46.0544	$46.05	$46.05	$46.10
Purchase #3	$78.36	4.582%	$81.9505	$81.95	$81.95	$82.00
Purchase #4	$34.60	10.228%	$38.1389	$38.14	$38.15	$38.10
Purchase #5	$70.54	11.131%	$78.3918	$78.39	$78.40	$78.40
Purchase #6	$95.81	5.753%	$101.3219	$101.32	$101.30	$101.30
Purchase #7	$36.85	9.456%	$40.3345	$40.33	$40.35	$40.30
7 purchase totals =	$579.38		$619.8386	$619.83	$619.85	$619.80