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	$144.37	10.144%	$159.0149	$159.01	$159.00	$159.00
Purchase #2	$221.69	3.691%	$229.8726	$229.87	$229.85	$229.90
Purchase #3	$122.82	12.466%	$138.1307	$138.13	$138.15	$138.10
Purchase #4	$136.29	6.115%	$144.6241	$144.62	$144.60	$144.60
Purchase #5	$67.91	6.655%	$72.4294	$72.43	$72.45	$72.40
Purchase #6	$137.73	7.778%	$148.4426	$148.44	$148.45	$148.40
Purchase #7	$34.65	11.213%	$38.5353	$38.54	$38.55	$38.50
7 purchase totals =	$865.46		$931.0496	$931.04	$931.05	$930.90