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	$168.91	11.535%	$188.3938	$188.39	$188.40	$188.40
Purchase #2	$130.93	10.697%	$144.9356	$144.94	$144.95	$144.90
Purchase #3	$82.82	11.739%	$92.5422	$92.54	$92.55	$92.50
Purchase #4	$34.54	11.579%	$38.5394	$38.54	$38.55	$38.50
Purchase #5	$111.48	6.335%	$118.5423	$118.54	$118.55	$118.50
Purchase #6	$91.99	9.208%	$100.4604	$100.46	$100.45	$100.50
Purchase #7	$94.53	11.660%	$105.5522	$105.55	$105.55	$105.60
7 purchase totals =	$715.20		$788.9659	$788.96	$789.00	$788.90