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	$228.96	9.335%	$250.3334	$250.33	$250.35	$250.30
Purchase #2	$100.73	11.792%	$112.6081	$112.61	$112.60	$112.60
Purchase #3	$116.82	12.105%	$130.9611	$130.96	$130.95	$131.00
Purchase #4	$57.69	10.161%	$63.5519	$63.55	$63.55	$63.60
Purchase #5	$245.70	11.773%	$274.6263	$274.63	$274.65	$274.60
Purchase #6	$16.61	11.742%	$18.5603	$18.56	$18.55	$18.60
Purchase #7	$233.91	9.247%	$255.5397	$255.54	$255.55	$255.50
7 purchase totals =	$1,000.42		$1,106.1808	$1,106.18	$1,106.20	$1,106.20