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	$91.56	6.537%	$97.5453	$97.55	$97.55	$97.50
Purchase #2	$64.89	8.542%	$70.4329	$70.43	$70.45	$70.40
Purchase #3	$231.51	7.320%	$248.4565	$248.46	$248.45	$248.50
Purchase #4	$212.68	12.230%	$238.6908	$238.69	$238.70	$238.70
Purchase #5	$238.43	4.694%	$249.6219	$249.62	$249.60	$249.60
Purchase #6	$177.65	13.107%	$200.9346	$200.93	$200.95	$200.90
Purchase #7	$45.67	11.502%	$50.923	$50.92	$50.90	$50.90
7 purchase totals =	$1,062.39		$1,156.6050	$1,156.60	$1,156.60	$1,156.50