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	$53.31	12.110%	$59.7658	$59.77	$59.75	$59.80
Purchase #2	$78.30	13.834%	$89.132	$89.13	$89.15	$89.10
Purchase #3	$164.79	8.447%	$178.7098	$178.71	$178.70	$178.70
Purchase #4	$166.88	13.286%	$189.0517	$189.05	$189.05	$189.10
Purchase #5	$205.68	13.701%	$233.8602	$233.86	$233.85	$233.90
Purchase #6	$6.48	10.441%	$7.1566	$7.16	$7.15	$7.20
Purchase #7	$44.90	10.856%	$49.7743	$49.77	$49.75	$49.80
7 purchase totals =	$720.34		$807.4504	$807.45	$807.40	$807.60