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	$83.88	5.661%	$88.6284	$88.63	$88.65	$88.60
Purchase #2	$142.29	9.834%	$156.2828	$156.28	$156.30	$156.30
Purchase #3	$59.67	12.115%	$66.899	$66.90	$66.90	$66.90
Purchase #4	$222.49	12.735%	$250.8241	$250.82	$250.80	$250.80
Purchase #5	$36.28	4.659%	$37.9703	$37.97	$37.95	$38.00
Purchase #6	$126.67	3.406%	$130.9844	$130.98	$131.00	$131.00
Purchase #7	$9.88	7.139%	$10.5853	$10.59	$10.60	$10.60
7 purchase totals =	$681.16		$742.1743	$742.17	$742.20	$742.20