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	$19.30	11.315%	$21.4838	$21.48	$21.50	$21.50
Purchase #2	$152.51	10.430%	$168.4168	$168.42	$168.40	$168.40
Purchase #3	$203.71	10.407%	$224.9101	$224.91	$224.90	$224.90
Purchase #4	$91.48	12.446%	$102.8656	$102.87	$102.85	$102.90
Purchase #5	$83.30	8.331%	$90.2397	$90.24	$90.25	$90.20
Purchase #6	$81.83	13.195%	$92.6275	$92.63	$92.65	$92.60
Purchase #7	$243.68	11.640%	$272.0444	$272.04	$272.05	$272.00
7 purchase totals =	$875.81		$972.5879	$972.59	$972.60	$972.50