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	$10.81	10.293%	$11.9227	$11.92	$11.90	$11.90
Purchase #2	$138.53	10.351%	$152.8692	$152.87	$152.85	$152.90
Purchase #3	$83.32	7.582%	$89.6373	$89.64	$89.65	$89.60
Purchase #4	$116.60	4.440%	$121.777	$121.78	$121.80	$121.80
Purchase #5	$64.27	9.784%	$70.5582	$70.56	$70.55	$70.60
Purchase #6	$27.71	13.690%	$31.5035	$31.50	$31.50	$31.50
Purchase #7	$39.72	12.599%	$44.7243	$44.72	$44.70	$44.70
7 purchase totals =	$480.96		$522.9922	$522.99	$522.95	$523.00