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	$76.48	6.719%	$81.6187	$81.62	$81.60	$81.60
Purchase #2	$15.99	12.570%	$17.9999	$18.00	$18.00	$18.00
Purchase #3	$86.51	11.656%	$96.5936	$96.59	$96.60	$96.60
Purchase #4	$119.52	5.615%	$126.231	$126.23	$126.25	$126.20
Purchase #5	$9.70	7.307%	$10.4088	$10.41	$10.40	$10.40
Purchase #6	$250.93	9.698%	$275.2652	$275.27	$275.25	$275.30
Purchase #7	$53.64	10.808%	$59.4374	$59.44	$59.45	$59.40
7 purchase totals =	$612.77		$667.5546	$667.56	$667.55	$667.50