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	$30.94	9.407%	$33.8505	$33.85	$33.85	$33.90
Purchase #2	$242.61	12.504%	$272.946	$272.95	$272.95	$272.90
Purchase #3	$23.56	4.462%	$24.6112	$24.61	$24.60	$24.60
Purchase #4	$57.34	9.651%	$62.8739	$62.87	$62.85	$62.90
Purchase #5	$28.34	10.489%	$31.3126	$31.31	$31.30	$31.30
Purchase #6	$94.78	6.227%	$100.682	$100.68	$100.70	$100.70
Purchase #7	$26.63	6.723%	$28.4203	$28.42	$28.40	$28.40
7 purchase totals =	$504.20		$554.6965	$554.69	$554.65	$554.70