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	$34.47	10.382%	$38.0487	$38.05	$38.05	$38.00
Purchase #2	$142.81	5.346%	$150.4446	$150.44	$150.45	$150.40
Purchase #3	$241.78	8.627%	$262.6384	$262.64	$262.65	$262.60
Purchase #4	$222.40	7.119%	$238.2327	$238.23	$238.25	$238.20
Purchase #5	$26.88	9.144%	$29.3379	$29.34	$29.35	$29.30
Purchase #6	$122.66	13.444%	$139.1504	$139.15	$139.15	$139.20
Purchase #7	$39.66	6.582%	$42.2704	$42.27	$42.25	$42.30
7 purchase totals =	$830.66		$900.1231	$900.12	$900.15	$900.00