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	$199.96	4.791%	$209.5401	$209.54	$209.55	$209.50
Purchase #2	$89.63	10.296%	$98.8583	$98.86	$98.85	$98.90
Purchase #3	$241.96	4.555%	$252.9813	$252.98	$253.00	$253.00
Purchase #4	$99.32	13.236%	$112.466	$112.47	$112.45	$112.50
Purchase #5	$172.54	8.732%	$187.6062	$187.61	$187.60	$187.60
Purchase #6	$175.29	6.773%	$187.1624	$187.16	$187.15	$187.20
Purchase #7	$27.53	4.472%	$28.7611	$28.76	$28.75	$28.80
7 purchase totals =	$1,006.23		$1,077.3754	$1,077.38	$1,077.35	$1,077.50