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	$50.48	5.141%	$53.0752	$53.08	$53.10	$53.10
Purchase #2	$67.33	7.349%	$72.2781	$72.28	$72.30	$72.30
Purchase #3	$205.40	5.719%	$217.1468	$217.15	$217.15	$217.10
Purchase #4	$133.70	12.416%	$150.3002	$150.30	$150.30	$150.30
Purchase #5	$138.78	10.341%	$153.1312	$153.13	$153.15	$153.10
Purchase #6	$86.62	6.745%	$92.4625	$92.46	$92.45	$92.50
Purchase #7	$88.90	13.834%	$101.1984	$101.20	$101.20	$101.20
7 purchase totals =	$771.21		$839.5924	$839.60	$839.65	$839.60