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	$80.82	10.619%	$89.4023	$89.40	$89.40	$89.40
Purchase #2	$128.88	7.377%	$138.3875	$138.39	$138.40	$138.40
Purchase #3	$27.53	11.191%	$30.6109	$30.61	$30.60	$30.60
Purchase #4	$157.93	4.442%	$164.9453	$164.95	$164.95	$164.90
Purchase #5	$56.87	10.870%	$63.0518	$63.05	$63.05	$63.10
Purchase #6	$192.27	6.695%	$205.1425	$205.14	$205.15	$205.10
Purchase #7	$127.40	3.142%	$131.4029	$131.40	$131.40	$131.40
7 purchase totals =	$771.70		$822.9432	$822.94	$822.95	$822.90