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	$219.95	13.581%	$249.8214	$249.82	$249.80	$249.80
Purchase #2	$53.35	5.109%	$56.0757	$56.08	$56.10	$56.10
Purchase #3	$111.27	9.147%	$121.4479	$121.45	$121.45	$121.40
Purchase #4	$178.89	6.858%	$191.1583	$191.16	$191.15	$191.20
Purchase #5	$65.47	10.334%	$72.2357	$72.24	$72.25	$72.20
Purchase #6	$98.85	5.803%	$104.5863	$104.59	$104.60	$104.60
Purchase #7	$12.64	6.188%	$13.4222	$13.42	$13.40	$13.40
7 purchase totals =	$740.42		$808.7475	$808.76	$808.75	$808.70