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	$85.62	4.302%	$89.3034	$89.30	$89.30	$89.30
Purchase #2	$220.39	5.831%	$233.2409	$233.24	$233.25	$233.20
Purchase #3	$38.50	4.316%	$40.1617	$40.16	$40.15	$40.20
Purchase #4	$137.36	13.542%	$155.9613	$155.96	$155.95	$156.00
Purchase #5	$118.54	6.156%	$125.8373	$125.84	$125.85	$125.80
Purchase #6	$11.97	6.721%	$12.7745	$12.77	$12.75	$12.80
Purchase #7	$61.89	7.243%	$66.3727	$66.37	$66.35	$66.40
7 purchase totals =	$674.27		$723.6518	$723.64	$723.60	$723.70