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	$26.63	12.405%	$29.9335	$29.93	$29.95	$29.90
Purchase #2	$100.29	13.244%	$113.5724	$113.57	$113.55	$113.60
Purchase #3	$129.31	13.591%	$146.8845	$146.88	$146.90	$146.90
Purchase #4	$66.82	5.396%	$70.4256	$70.43	$70.45	$70.40
Purchase #5	$93.93	10.612%	$103.8979	$103.90	$103.90	$103.90
Purchase #6	$194.43	9.529%	$212.9572	$212.96	$212.95	$213.00
Purchase #7	$98.43	10.530%	$108.7947	$108.79	$108.80	$108.80
7 purchase totals =	$709.84		$786.4658	$786.46	$786.50	$786.50