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	$63.25	6.539%	$67.3859	$67.39	$67.40	$67.40
Purchase #2	$133.27	9.590%	$146.0506	$146.05	$146.05	$146.10
Purchase #3	$123.96	8.451%	$134.4359	$134.44	$134.45	$134.40
Purchase #4	$83.71	3.157%	$86.3527	$86.35	$86.35	$86.40
Purchase #5	$70.72	13.784%	$80.468	$80.47	$80.45	$80.50
Purchase #6	$5.83	4.821%	$6.1111	$6.11	$6.10	$6.10
Purchase #7	$85.82	6.113%	$91.0662	$91.07	$91.05	$91.10
7 purchase totals =	$566.56		$611.8704	$611.88	$611.85	$612.00