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	$121.97	3.831%	$126.6427	$126.64	$126.65	$126.60
Purchase #2	$210.99	7.530%	$226.8775	$226.88	$226.90	$226.90
Purchase #3	$19.44	8.818%	$21.1542	$21.15	$21.15	$21.20
Purchase #4	$81.89	10.230%	$90.2673	$90.27	$90.25	$90.30
Purchase #5	$88.40	12.569%	$99.511	$99.51	$99.50	$99.50
Purchase #6	$50.43	9.845%	$55.3948	$55.39	$55.40	$55.40
Purchase #7	$46.64	6.660%	$49.7462	$49.75	$49.75	$49.70
7 purchase totals =	$619.76		$669.5937	$669.59	$669.60	$669.60