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	$48.74	3.295%	$50.346	$50.35	$50.35	$50.30
Purchase #2	$75.83	10.306%	$83.645	$83.65	$83.65	$83.60
Purchase #3	$20.90	4.417%	$21.8232	$21.82	$21.80	$21.80
Purchase #4	$172.53	10.574%	$190.7733	$190.77	$190.75	$190.80
Purchase #5	$235.39	8.788%	$256.0761	$256.08	$256.10	$256.10
Purchase #6	$92.31	12.685%	$104.0195	$104.02	$104.00	$104.00
Purchase #7	$141.90	9.245%	$155.0187	$155.02	$155.00	$155.00
7 purchase totals =	$787.60		$861.7018	$861.71	$861.65	$861.60