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	$126.67	5.247%	$133.3164	$133.32	$133.30	$133.30
Purchase #2	$90.41	10.151%	$99.5875	$99.59	$99.60	$99.60
Purchase #3	$26.56	10.803%	$29.4293	$29.43	$29.45	$29.40
Purchase #4	$98.65	12.732%	$111.2101	$111.21	$111.20	$111.20
Purchase #5	$141.97	10.759%	$157.2446	$157.24	$157.25	$157.20
Purchase #6	$160.41	12.546%	$180.535	$180.54	$180.55	$180.50
Purchase #7	$96.86	5.699%	$102.3801	$102.38	$102.40	$102.40
7 purchase totals =	$741.53		$813.7030	$813.71	$813.75	$813.60