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	$16.58	9.348%	$18.1299	$18.13	$18.15	$18.10
Purchase #2	$188.47	4.460%	$196.8758	$196.88	$196.90	$196.90
Purchase #3	$184.31	4.547%	$192.6906	$192.69	$192.70	$192.70
Purchase #4	$116.97	11.647%	$130.5935	$130.59	$130.60	$130.60
Purchase #5	$118.68	8.364%	$128.6064	$128.61	$128.60	$128.60
Purchase #6	$118.37	13.688%	$134.5725	$134.57	$134.55	$134.60
Purchase #7	$146.50	9.242%	$160.0395	$160.04	$160.05	$160.00
7 purchase totals =	$889.88		$961.5082	$961.51	$961.55	$961.50