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	$83.30	7.418%	$89.4792	$89.48	$89.50	$89.50
Purchase #2	$10.89	7.686%	$11.727	$11.73	$11.75	$11.70
Purchase #3	$234.89	6.665%	$250.5454	$250.55	$250.55	$250.50
Purchase #4	$39.91	4.320%	$41.6341	$41.63	$41.65	$41.60
Purchase #5	$36.95	7.119%	$39.5805	$39.58	$39.60	$39.60
Purchase #6	$9.80	11.776%	$10.954	$10.95	$10.95	$11.00
Purchase #7	$155.51	6.328%	$165.3507	$165.35	$165.35	$165.40
7 purchase totals =	$571.25		$609.2709	$609.27	$609.35	$609.30