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	$126.74	6.335%	$134.769	$134.77	$134.75	$134.80
Purchase #2	$45.88	9.661%	$50.3125	$50.31	$50.30	$50.30
Purchase #3	$164.91	8.866%	$179.5309	$179.53	$179.55	$179.50
Purchase #4	$43.88	11.292%	$48.8349	$48.83	$48.85	$48.80
Purchase #5	$92.74	10.558%	$102.5315	$102.53	$102.55	$102.50
Purchase #6	$72.60	7.866%	$78.3107	$78.31	$78.30	$78.30
Purchase #7	$15.86	13.844%	$18.0557	$18.06	$18.05	$18.10
7 purchase totals =	$562.61		$612.3452	$612.34	$612.35	$612.30