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	$18.49	7.509%	$19.8784	$19.88	$19.90	$19.90
Purchase #2	$148.91	5.136%	$156.558	$156.56	$156.55	$156.60
Purchase #3	$123.77	11.171%	$137.5963	$137.60	$137.60	$137.60
Purchase #4	$132.36	9.440%	$144.8548	$144.85	$144.85	$144.90
Purchase #5	$246.76	7.221%	$264.5785	$264.58	$264.60	$264.60
Purchase #6	$141.87	7.873%	$153.0394	$153.04	$153.05	$153.00
Purchase #7	$50.51	13.494%	$57.3258	$57.33	$57.35	$57.30
7 purchase totals =	$862.67		$933.8312	$933.84	$933.90	$933.90