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	$63.82	11.321%	$71.0451	$71.05	$71.05	$71.00
Purchase #2	$130.66	3.429%	$135.1403	$135.14	$135.15	$135.10
Purchase #3	$93.53	9.613%	$102.521	$102.52	$102.50	$102.50
Purchase #4	$78.60	13.324%	$89.0727	$89.07	$89.05	$89.10
Purchase #5	$158.43	7.337%	$170.054	$170.05	$170.05	$170.10
Purchase #6	$50.67	12.629%	$57.0691	$57.07	$57.05	$57.10
Purchase #7	$210.29	13.309%	$238.2775	$238.28	$238.30	$238.30
7 purchase totals =	$786.00		$863.1797	$863.18	$863.15	$863.20