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	$92.45	5.810%	$97.8213	$97.82	$97.80	$97.80
Purchase #2	$133.91	6.622%	$142.7775	$142.78	$142.80	$142.80
Purchase #3	$100.49	11.383%	$111.9288	$111.93	$111.95	$111.90
Purchase #4	$222.49	12.175%	$249.5782	$249.58	$249.60	$249.60
Purchase #5	$28.96	7.525%	$31.1392	$31.14	$31.15	$31.10
Purchase #6	$108.34	8.190%	$117.213	$117.21	$117.20	$117.20
Purchase #7	$72.72	6.416%	$77.3857	$77.39	$77.40	$77.40
7 purchase totals =	$759.36		$827.8437	$827.85	$827.90	$827.80