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	$109.78	8.269%	$118.8577	$118.86	$118.85	$118.90
Purchase #2	$45.50	12.592%	$51.2294	$51.23	$51.25	$51.20
Purchase #3	$198.28	12.510%	$223.0848	$223.08	$223.10	$223.10
Purchase #4	$48.93	13.595%	$55.582	$55.58	$55.60	$55.60
Purchase #5	$81.90	12.329%	$91.9975	$92.00	$92.00	$92.00
Purchase #6	$244.96	3.718%	$254.0676	$254.07	$254.05	$254.10
Purchase #7	$57.50	13.111%	$65.0388	$65.04	$65.05	$65.00
7 purchase totals =	$786.85		$859.8578	$859.86	$859.90	$859.90