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	$38.59	12.441%	$43.391	$43.39	$43.40	$43.40
Purchase #2	$103.79	7.316%	$111.3833	$111.38	$111.40	$111.40
Purchase #3	$133.47	3.267%	$137.8305	$137.83	$137.85	$137.80
Purchase #4	$91.64	13.636%	$104.136	$104.14	$104.15	$104.10
Purchase #5	$137.98	13.248%	$156.2596	$156.26	$156.25	$156.30
Purchase #6	$34.31	13.195%	$38.8372	$38.84	$38.85	$38.80
Purchase #7	$152.55	13.106%	$172.5432	$172.54	$172.55	$172.50
7 purchase totals =	$692.33		$764.3808	$764.38	$764.45	$764.30