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	$16.83	12.550%	$18.9422	$18.94	$18.95	$18.90
Purchase #2	$220.51	12.368%	$247.7827	$247.78	$247.80	$247.80
Purchase #3	$90.61	10.244%	$99.8921	$99.89	$99.90	$99.90
Purchase #4	$118.35	11.292%	$131.7141	$131.71	$131.70	$131.70
Purchase #5	$201.43	13.291%	$228.2021	$228.20	$228.20	$228.20
Purchase #6	$226.56	6.537%	$241.3702	$241.37	$241.35	$241.40
Purchase #7	$158.70	10.614%	$175.5444	$175.54	$175.55	$175.50
7 purchase totals =	$1,032.99		$1,143.4478	$1,143.43	$1,143.45	$1,143.40