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	$127.88	7.816%	$137.8751	$137.88	$137.90	$137.90
Purchase #2	$105.76	11.172%	$117.5755	$117.58	$117.60	$117.60
Purchase #3	$246.57	13.355%	$279.4994	$279.50	$279.50	$279.50
Purchase #4	$198.63	12.607%	$223.6713	$223.67	$223.65	$223.70
Purchase #5	$236.88	12.665%	$266.8809	$266.88	$266.90	$266.90
Purchase #6	$61.32	5.109%	$64.4528	$64.45	$64.45	$64.50
Purchase #7	$165.67	13.115%	$187.3976	$187.40	$187.40	$187.40
7 purchase totals =	$1,142.71		$1,277.3526	$1,277.36	$1,277.40	$1,277.50