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	$29.86	8.769%	$32.4784	$32.48	$32.50	$32.50
Purchase #2	$97.86	13.496%	$111.0672	$111.07	$111.05	$111.10
Purchase #3	$96.97	8.666%	$105.3734	$105.37	$105.35	$105.40
Purchase #4	$49.49	10.532%	$54.7023	$54.70	$54.70	$54.70
Purchase #5	$245.95	13.480%	$279.1041	$279.10	$279.10	$279.10
Purchase #6	$132.80	9.645%	$145.6086	$145.61	$145.60	$145.60
Purchase #7	$175.34	11.854%	$196.1248	$196.12	$196.10	$196.10
7 purchase totals =	$828.27		$924.4588	$924.45	$924.40	$924.50