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	$139.96	13.833%	$159.3207	$159.32	$159.30	$159.30
Purchase #2	$222.25	7.123%	$238.0809	$238.08	$238.10	$238.10
Purchase #3	$137.43	9.571%	$150.5834	$150.58	$150.60	$150.60
Purchase #4	$152.63	4.712%	$159.8219	$159.82	$159.80	$159.80
Purchase #5	$223.82	9.215%	$244.445	$244.45	$244.45	$244.40
Purchase #6	$52.67	5.608%	$55.6237	$55.62	$55.60	$55.60
Purchase #7	$224.63	13.372%	$254.6675	$254.67	$254.65	$254.70
7 purchase totals =	$1,153.39		$1,262.5431	$1,262.54	$1,262.50	$1,262.50