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	$198.74	5.379%	$209.4302	$209.43	$209.45	$209.40
Purchase #2	$14.40	4.301%	$15.0193	$15.02	$15.00	$15.00
Purchase #3	$110.76	10.638%	$122.5426	$122.54	$122.55	$122.50
Purchase #4	$87.86	12.470%	$98.8161	$98.82	$98.80	$98.80
Purchase #5	$165.30	4.423%	$172.6112	$172.61	$172.60	$172.60
Purchase #6	$97.85	7.798%	$105.4803	$105.48	$105.50	$105.50
Purchase #7	$49.66	9.790%	$54.5217	$54.52	$54.50	$54.50
7 purchase totals =	$724.57		$778.4214	$778.42	$778.40	$778.30