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	$99.40	12.262%	$111.5884	$111.59	$111.60	$111.60
Purchase #2	$105.37	8.143%	$113.9503	$113.95	$113.95	$114.00
Purchase #3	$49.79	8.176%	$53.8608	$53.86	$53.85	$53.90
Purchase #4	$82.72	13.544%	$93.9236	$93.92	$93.90	$93.90
Purchase #5	$92.88	10.499%	$102.6315	$102.63	$102.65	$102.60
Purchase #6	$24.51	9.556%	$26.8522	$26.85	$26.85	$26.90
Purchase #7	$169.31	10.189%	$186.561	$186.56	$186.55	$186.60
7 purchase totals =	$623.98		$689.3678	$689.36	$689.35	$689.50