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	$100.43	8.441%	$108.9073	$108.91	$108.90	$108.90
Purchase #2	$238.70	3.854%	$247.8995	$247.90	$247.90	$247.90
Purchase #3	$227.84	5.615%	$240.6332	$240.63	$240.65	$240.60
Purchase #4	$114.95	11.710%	$128.4106	$128.41	$128.40	$128.40
Purchase #5	$77.63	10.244%	$85.5824	$85.58	$85.60	$85.60
Purchase #6	$142.41	5.742%	$150.5872	$150.59	$150.60	$150.60
Purchase #7	$93.79	13.863%	$106.7921	$106.79	$106.80	$106.80
7 purchase totals =	$995.75		$1,068.8123	$1,068.81	$1,068.85	$1,068.80