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	$52.92	5.827%	$56.0036	$56.00	$56.00	$56.00
Purchase #2	$5.95	7.607%	$6.4026	$6.40	$6.40	$6.40
Purchase #3	$156.92	9.856%	$172.386	$172.39	$172.40	$172.40
Purchase #4	$165.76	13.553%	$188.2255	$188.23	$188.25	$188.20
Purchase #5	$59.66	8.288%	$64.6046	$64.60	$64.60	$64.60
Purchase #6	$89.93	6.291%	$95.5875	$95.59	$95.60	$95.60
Purchase #7	$190.94	9.158%	$208.4263	$208.43	$208.45	$208.40
7 purchase totals =	$722.08		$791.6361	$791.64	$791.70	$791.60