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	$94.38	6.580%	$100.5902	$100.59	$100.60	$100.60
Purchase #2	$207.81	4.696%	$217.5688	$217.57	$217.55	$217.60
Purchase #3	$88.28	13.527%	$100.2216	$100.22	$100.20	$100.20
Purchase #4	$200.44	13.143%	$226.7838	$226.78	$226.80	$226.80
Purchase #5	$235.25	8.276%	$254.7193	$254.72	$254.70	$254.70
Purchase #6	$91.35	7.236%	$97.9601	$97.96	$97.95	$98.00
Purchase #7	$61.44	3.541%	$63.6156	$63.62	$63.60	$63.60
7 purchase totals =	$978.95		$1,061.4594	$1,061.46	$1,061.40	$1,061.50