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	$21.71	12.617%	$24.4492	$24.45	$24.45	$24.40
Purchase #2	$50.46	8.819%	$54.9101	$54.91	$54.90	$54.90
Purchase #3	$146.89	12.759%	$165.6317	$165.63	$165.65	$165.60
Purchase #4	$150.49	12.593%	$169.4412	$169.44	$169.45	$169.40
Purchase #5	$52.50	12.706%	$59.1707	$59.17	$59.15	$59.20
Purchase #6	$101.87	12.575%	$114.6802	$114.68	$114.70	$114.70
Purchase #7	$230.79	3.813%	$239.59	$239.59	$239.60	$239.60
7 purchase totals =	$754.71		$827.8731	$827.87	$827.90	$827.80