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	$34.69	3.824%	$36.0165	$36.02	$36.00	$36.00
Purchase #2	$174.40	10.732%	$193.1166	$193.12	$193.10	$193.10
Purchase #3	$174.55	12.622%	$196.5817	$196.58	$196.60	$196.60
Purchase #4	$58.55	12.518%	$65.8793	$65.88	$65.90	$65.90
Purchase #5	$149.28	6.472%	$158.9414	$158.94	$158.95	$158.90
Purchase #6	$88.49	4.456%	$92.4331	$92.43	$92.45	$92.40
Purchase #7	$35.90	5.327%	$37.8124	$37.81	$37.80	$37.80
7 purchase totals =	$715.86		$780.7810	$780.78	$780.80	$780.70