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	$26.92	5.162%	$28.3096	$28.31	$28.30	$28.30
Purchase #2	$54.89	12.189%	$61.5805	$61.58	$61.60	$61.60
Purchase #3	$150.74	9.185%	$164.5855	$164.59	$164.60	$164.60
Purchase #4	$207.99	13.392%	$235.844	$235.84	$235.85	$235.80
Purchase #5	$116.93	6.494%	$124.5234	$124.52	$124.50	$124.50
Purchase #6	$73.84	11.340%	$82.2135	$82.21	$82.20	$82.20
Purchase #7	$80.81	11.851%	$90.3868	$90.39	$90.40	$90.40
7 purchase totals =	$712.12		$787.4433	$787.44	$787.45	$787.40