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	$70.45	11.226%	$78.3587	$78.36	$78.35	$78.40
Purchase #2	$186.85	7.437%	$200.746	$200.75	$200.75	$200.70
Purchase #3	$47.51	4.130%	$49.4722	$49.47	$49.45	$49.50
Purchase #4	$73.47	11.737%	$82.0932	$82.09	$82.10	$82.10
Purchase #5	$114.47	9.684%	$125.5553	$125.56	$125.55	$125.60
Purchase #6	$230.28	4.761%	$241.2436	$241.24	$241.25	$241.20
Purchase #7	$20.97	4.190%	$21.8486	$21.85	$21.85	$21.80
7 purchase totals =	$744.00		$799.3176	$799.32	$799.30	$799.30