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	$16.40	11.395%	$18.2688	$18.27	$18.25	$18.30
Purchase #2	$142.68	12.151%	$160.017	$160.02	$160.00	$160.00
Purchase #3	$183.43	3.850%	$190.4921	$190.49	$190.50	$190.50
Purchase #4	$138.84	8.110%	$150.0999	$150.10	$150.10	$150.10
Purchase #5	$128.66	12.759%	$145.0757	$145.08	$145.10	$145.10
Purchase #6	$147.59	8.816%	$160.6015	$160.60	$160.60	$160.60
Purchase #7	$162.69	3.643%	$168.6168	$168.62	$168.60	$168.60
7 purchase totals =	$920.29		$993.1718	$993.18	$993.15	$993.20