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	$241.76	12.347%	$271.6101	$271.61	$271.60	$271.60
Purchase #2	$224.33	10.465%	$247.8061	$247.81	$247.80	$247.80
Purchase #3	$243.41	8.406%	$263.871	$263.87	$263.85	$263.90
Purchase #4	$53.95	13.105%	$61.0201	$61.02	$61.00	$61.00
Purchase #5	$27.51	7.131%	$29.4717	$29.47	$29.45	$29.50
Purchase #6	$35.65	6.403%	$37.9327	$37.93	$37.95	$37.90
Purchase #7	$83.29	13.181%	$94.2685	$94.27	$94.25	$94.30
7 purchase totals =	$909.90		$1,005.9802	$1,005.98	$1,005.90	$1,006.00