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	$215.25	10.853%	$238.6111	$238.61	$238.60	$238.60
Purchase #2	$64.92	9.446%	$71.0523	$71.05	$71.05	$71.10
Purchase #3	$24.68	12.804%	$27.84	$27.84	$27.85	$27.80
Purchase #4	$190.33	12.450%	$214.0261	$214.03	$214.05	$214.00
Purchase #5	$91.51	12.137%	$102.6166	$102.62	$102.60	$102.60
Purchase #6	$81.50	9.556%	$89.2881	$89.29	$89.30	$89.30
Purchase #7	$177.70	10.523%	$196.3994	$196.40	$196.40	$196.40
7 purchase totals =	$845.89		$939.8336	$939.84	$939.85	$939.80