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	$124.78	10.195%	$137.5013	$137.50	$137.50	$137.50
Purchase #2	$91.84	9.848%	$100.8844	$100.88	$100.90	$100.90
Purchase #3	$106.69	3.622%	$110.5543	$110.55	$110.55	$110.60
Purchase #4	$29.97	8.156%	$32.4144	$32.41	$32.40	$32.40
Purchase #5	$53.48	12.631%	$60.2351	$60.24	$60.25	$60.20
Purchase #6	$56.71	11.545%	$63.2572	$63.26	$63.25	$63.30
Purchase #7	$230.42	10.764%	$255.2224	$255.22	$255.20	$255.20
7 purchase totals =	$693.89		$760.0691	$760.06	$760.05	$760.10