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	$142.32	13.170%	$161.0635	$161.06	$161.05	$161.10
Purchase #2	$222.28	10.822%	$246.3351	$246.34	$246.35	$246.30
Purchase #3	$90.85	7.156%	$97.3512	$97.35	$97.35	$97.40
Purchase #4	$108.80	13.121%	$123.0756	$123.08	$123.10	$123.10
Purchase #5	$166.27	12.480%	$187.0205	$187.02	$187.00	$187.00
Purchase #6	$110.30	10.230%	$121.5837	$121.58	$121.60	$121.60
Purchase #7	$37.77	12.287%	$42.4108	$42.41	$42.40	$42.40
7 purchase totals =	$878.59		$978.8404	$978.84	$978.85	$978.90