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	$13.91	10.623%	$15.3877	$15.39	$15.40	$15.40
Purchase #2	$230.52	5.155%	$242.4033	$242.40	$242.40	$242.40
Purchase #3	$53.97	10.544%	$59.6606	$59.66	$59.65	$59.70
Purchase #4	$156.96	8.124%	$169.7114	$169.71	$169.70	$169.70
Purchase #5	$102.63	8.294%	$111.1421	$111.14	$111.15	$111.10
Purchase #6	$123.74	8.338%	$134.0574	$134.06	$134.05	$134.10
Purchase #7	$235.56	11.436%	$262.4986	$262.50	$262.50	$262.50
7 purchase totals =	$917.29		$994.8611	$994.86	$994.85	$994.90