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	$231.95	5.131%	$243.8514	$243.85	$243.85	$243.90
Purchase #2	$128.49	9.288%	$140.4242	$140.42	$140.40	$140.40
Purchase #3	$32.36	5.375%	$34.0994	$34.10	$34.10	$34.10
Purchase #4	$32.45	13.403%	$36.7993	$36.80	$36.80	$36.80
Purchase #5	$83.64	7.385%	$89.8168	$89.82	$89.80	$89.80
Purchase #6	$83.77	4.189%	$87.2791	$87.28	$87.30	$87.30
Purchase #7	$33.87	9.334%	$37.0314	$37.03	$37.05	$37.00
7 purchase totals =	$626.53		$669.3016	$669.30	$669.30	$669.30