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	$169.31	11.813%	$189.3106	$189.31	$189.30	$189.30
Purchase #2	$123.77	8.309%	$134.054	$134.05	$134.05	$134.10
Purchase #3	$148.87	4.849%	$156.0887	$156.09	$156.10	$156.10
Purchase #4	$241.91	6.406%	$257.4068	$257.41	$257.40	$257.40
Purchase #5	$191.31	4.326%	$199.5861	$199.59	$199.60	$199.60
Purchase #6	$95.91	9.600%	$105.1174	$105.12	$105.10	$105.10
Purchase #7	$51.81	13.493%	$58.8007	$58.80	$58.80	$58.80
7 purchase totals =	$1,022.89		$1,100.3643	$1,100.37	$1,100.35	$1,100.40