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	$14.76	12.333%	$16.5804	$16.58	$16.60	$16.60
Purchase #2	$241.78	11.813%	$270.3415	$270.34	$270.35	$270.30
Purchase #3	$11.83	10.215%	$13.0384	$13.04	$13.05	$13.00
Purchase #4	$41.33	11.157%	$45.9412	$45.94	$45.95	$45.90
Purchase #5	$47.55	11.824%	$53.1723	$53.17	$53.15	$53.20
Purchase #6	$27.30	5.515%	$28.8056	$28.81	$28.80	$28.80
Purchase #7	$59.31	13.763%	$67.4728	$67.47	$67.45	$67.50
7 purchase totals =	$443.86		$495.3522	$495.35	$495.35	$495.30