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	$138.85	12.107%	$155.6606	$155.66	$155.65	$155.70
Purchase #2	$50.78	8.733%	$55.2146	$55.21	$55.20	$55.20
Purchase #3	$190.85	3.176%	$196.9114	$196.91	$196.90	$196.90
Purchase #4	$154.77	6.497%	$164.8254	$164.83	$164.85	$164.80
Purchase #5	$238.68	7.306%	$256.118	$256.12	$256.10	$256.10
Purchase #6	$245.52	8.184%	$265.6134	$265.61	$265.60	$265.60
Purchase #7	$163.87	8.811%	$178.3086	$178.31	$178.30	$178.30
7 purchase totals =	$1,183.32		$1,272.6520	$1,272.65	$1,272.60	$1,272.60