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	$102.90	5.466%	$108.5245	$108.52	$108.50	$108.50
Purchase #2	$98.96	12.187%	$111.0203	$111.02	$111.00	$111.00
Purchase #3	$88.85	4.178%	$92.5622	$92.56	$92.55	$92.60
Purchase #4	$195.41	5.739%	$206.6246	$206.62	$206.60	$206.60
Purchase #5	$101.32	6.204%	$107.6059	$107.61	$107.60	$107.60
Purchase #6	$59.72	13.492%	$67.7774	$67.78	$67.80	$67.80
Purchase #7	$55.80	6.835%	$59.6139	$59.61	$59.60	$59.60
7 purchase totals =	$702.96		$753.7288	$753.72	$753.65	$753.70