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	$112.56	13.360%	$127.598	$127.60	$127.60	$127.60
Purchase #2	$183.55	9.195%	$200.4274	$200.43	$200.45	$200.40
Purchase #3	$240.93	5.516%	$254.2197	$254.22	$254.20	$254.20
Purchase #4	$49.92	3.402%	$51.6183	$51.62	$51.60	$51.60
Purchase #5	$149.87	10.689%	$165.8896	$165.89	$165.90	$165.90
Purchase #6	$67.88	7.367%	$72.8807	$72.88	$72.90	$72.90
Purchase #7	$78.57	7.548%	$84.5005	$84.50	$84.50	$84.50
7 purchase totals =	$883.28		$957.1342	$957.14	$957.15	$957.10