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	$185.99	3.127%	$191.8059	$191.81	$191.80	$191.80
Purchase #2	$87.87	13.153%	$99.4275	$99.43	$99.45	$99.40
Purchase #3	$156.97	11.397%	$174.8599	$174.86	$174.85	$174.90
Purchase #4	$24.72	12.784%	$27.8802	$27.88	$27.90	$27.90
Purchase #5	$171.38	11.679%	$191.3955	$191.40	$191.40	$191.40
Purchase #6	$161.80	7.257%	$173.5418	$173.54	$173.55	$173.50
Purchase #7	$75.56	6.495%	$80.4676	$80.47	$80.45	$80.50
7 purchase totals =	$864.29		$939.3784	$939.39	$939.40	$939.40