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	$83.82	7.467%	$90.0788	$90.08	$90.10	$90.10
Purchase #2	$42.79	12.397%	$48.0947	$48.09	$48.10	$48.10
Purchase #3	$108.57	11.483%	$121.0371	$121.04	$121.05	$121.00
Purchase #4	$220.25	10.289%	$242.9115	$242.91	$242.90	$242.90
Purchase #5	$153.73	12.104%	$172.3375	$172.34	$172.35	$172.30
Purchase #6	$25.72	8.461%	$27.8962	$27.90	$27.90	$27.90
Purchase #7	$90.64	9.710%	$99.4411	$99.44	$99.45	$99.40
7 purchase totals =	$725.52		$801.7969	$801.80	$801.85	$801.70