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	$21.49	6.532%	$22.8937	$22.89	$22.90	$22.90
Purchase #2	$161.50	11.402%	$179.9142	$179.91	$179.90	$179.90
Purchase #3	$38.83	10.603%	$42.9471	$42.95	$42.95	$42.90
Purchase #4	$90.98	8.205%	$98.4449	$98.44	$98.45	$98.40
Purchase #5	$99.74	12.262%	$111.9701	$111.97	$111.95	$112.00
Purchase #6	$164.76	8.152%	$178.1912	$178.19	$178.20	$178.20
Purchase #7	$128.56	3.126%	$132.5788	$132.58	$132.60	$132.60
7 purchase totals =	$705.86		$766.9400	$766.93	$766.95	$766.90