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	$113.35	13.488%	$128.6386	$128.64	$128.65	$128.60
Purchase #2	$196.72	10.866%	$218.0956	$218.10	$218.10	$218.10
Purchase #3	$69.90	4.435%	$73.0001	$73.00	$73.00	$73.00
Purchase #4	$91.63	5.377%	$96.5569	$96.56	$96.55	$96.60
Purchase #5	$64.82	3.177%	$66.8793	$66.88	$66.90	$66.90
Purchase #6	$62.25	4.225%	$64.8801	$64.88	$64.90	$64.90
Purchase #7	$100.60	13.168%	$113.847	$113.85	$113.85	$113.80
7 purchase totals =	$699.27		$761.8976	$761.91	$761.95	$761.90