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	$99.78	5.845%	$105.6121	$105.61	$105.60	$105.60
Purchase #2	$177.98	5.220%	$187.2706	$187.27	$187.25	$187.30
Purchase #3	$73.52	9.871%	$80.7772	$80.78	$80.80	$80.80
Purchase #4	$71.80	6.398%	$76.3938	$76.39	$76.40	$76.40
Purchase #5	$213.64	8.297%	$231.3657	$231.37	$231.35	$231.40
Purchase #6	$29.94	7.443%	$32.1684	$32.17	$32.15	$32.20
Purchase #7	$113.99	11.748%	$127.3815	$127.38	$127.40	$127.40
7 purchase totals =	$780.65		$840.9693	$840.97	$840.95	$841.10