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	$71.51	9.459%	$78.2741	$78.27	$78.25	$78.30
Purchase #2	$42.68	13.561%	$48.4678	$48.47	$48.45	$48.50
Purchase #3	$231.37	10.872%	$256.5245	$256.52	$256.50	$256.50
Purchase #4	$82.42	7.798%	$88.8471	$88.85	$88.85	$88.80
Purchase #5	$144.54	3.127%	$149.0598	$149.06	$149.05	$149.10
Purchase #6	$63.97	12.467%	$71.9451	$71.95	$71.95	$71.90
Purchase #7	$74.43	8.252%	$80.572	$80.57	$80.55	$80.60
7 purchase totals =	$710.92		$773.6904	$773.69	$773.60	$773.70