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	$12.72	8.626%	$13.8172	$13.82	$13.80	$13.80
Purchase #2	$106.72	4.450%	$111.469	$111.47	$111.45	$111.50
Purchase #3	$40.65	7.781%	$43.813	$43.81	$43.80	$43.80
Purchase #4	$86.69	11.136%	$96.3438	$96.34	$96.35	$96.30
Purchase #5	$131.45	4.866%	$137.8464	$137.85	$137.85	$137.80
Purchase #6	$207.96	10.456%	$229.7043	$229.70	$229.70	$229.70
Purchase #7	$174.83	3.487%	$180.9263	$180.93	$180.95	$180.90
7 purchase totals =	$761.02		$813.9200	$813.92	$813.90	$813.80