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	$169.72	4.577%	$177.4881	$177.49	$177.50	$177.50
Purchase #2	$101.63	12.409%	$114.2413	$114.24	$114.25	$114.20
Purchase #3	$79.92	8.345%	$86.5893	$86.59	$86.60	$86.60
Purchase #4	$147.84	5.772%	$156.3733	$156.37	$156.35	$156.40
Purchase #5	$98.59	4.697%	$103.2208	$103.22	$103.20	$103.20
Purchase #6	$69.57	3.583%	$72.0627	$72.06	$72.05	$72.10
Purchase #7	$192.94	10.340%	$212.89	$212.89	$212.90	$212.90
7 purchase totals =	$860.21		$922.8655	$922.86	$922.85	$922.90