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	$134.43	7.135%	$144.0216	$144.02	$144.00	$144.00
Purchase #2	$115.60	6.235%	$122.8077	$122.81	$122.80	$122.80
Purchase #3	$90.98	3.737%	$94.3799	$94.38	$94.40	$94.40
Purchase #4	$152.38	6.691%	$162.5757	$162.58	$162.60	$162.60
Purchase #5	$64.83	11.601%	$72.3509	$72.35	$72.35	$72.40
Purchase #6	$19.50	4.586%	$20.3943	$20.39	$20.40	$20.40
Purchase #7	$153.46	10.541%	$169.6362	$169.64	$169.65	$169.60
7 purchase totals =	$731.18		$786.1663	$786.17	$786.20	$786.20