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	$221.57	5.853%	$234.5385	$234.54	$234.55	$234.50
Purchase #2	$45.37	10.329%	$50.0563	$50.06	$50.05	$50.10
Purchase #3	$54.82	12.768%	$61.8194	$61.82	$61.80	$61.80
Purchase #4	$47.86	13.276%	$54.2139	$54.21	$54.20	$54.20
Purchase #5	$12.98	3.658%	$13.4548	$13.45	$13.45	$13.50
Purchase #6	$124.79	12.248%	$140.0743	$140.07	$140.05	$140.10
Purchase #7	$85.28	4.513%	$89.1287	$89.13	$89.15	$89.10
7 purchase totals =	$592.67		$643.2859	$643.28	$643.25	$643.30