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	$247.40	12.391%	$278.0553	$278.06	$278.05	$278.10
Purchase #2	$175.30	10.376%	$193.4891	$193.49	$193.50	$193.50
Purchase #3	$164.46	8.783%	$178.9045	$178.90	$178.90	$178.90
Purchase #4	$84.71	9.340%	$92.6219	$92.62	$92.60	$92.60
Purchase #5	$82.70	8.652%	$89.8552	$89.86	$89.85	$89.90
Purchase #6	$65.34	10.845%	$72.4261	$72.43	$72.45	$72.40
Purchase #7	$54.54	13.560%	$61.9356	$61.94	$61.95	$61.90
7 purchase totals =	$874.45		$967.2877	$967.30	$967.30	$967.30