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	$25.38	12.778%	$28.6231	$28.62	$28.60	$28.60
Purchase #2	$151.60	10.434%	$167.4179	$167.42	$167.40	$167.40
Purchase #3	$152.96	6.613%	$163.0752	$163.08	$163.10	$163.10
Purchase #4	$11.65	7.646%	$12.5408	$12.54	$12.55	$12.50
Purchase #5	$244.73	3.798%	$254.0248	$254.02	$254.00	$254.00
Purchase #6	$79.89	11.420%	$89.0134	$89.01	$89.00	$89.00
Purchase #7	$107.88	11.151%	$119.9097	$119.91	$119.90	$119.90
7 purchase totals =	$774.09		$834.6049	$834.60	$834.55	$834.50