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	$64.57	3.663%	$66.9352	$66.94	$66.95	$66.90
Purchase #2	$40.90	7.408%	$43.9299	$43.93	$43.95	$43.90
Purchase #3	$151.60	5.640%	$160.1502	$160.15	$160.15	$160.20
Purchase #4	$240.66	6.781%	$256.9792	$256.98	$257.00	$257.00
Purchase #5	$23.88	13.626%	$27.1339	$27.13	$27.15	$27.10
Purchase #6	$210.85	5.799%	$223.0772	$223.08	$223.10	$223.10
Purchase #7	$63.43	10.855%	$70.3153	$70.32	$70.30	$70.30
7 purchase totals =	$795.89		$848.5209	$848.53	$848.60	$848.50