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	$78.29	7.111%	$83.8572	$83.86	$83.85	$83.90
Purchase #2	$159.98	5.431%	$168.6685	$168.67	$168.65	$168.70
Purchase #3	$217.74	10.786%	$241.2254	$241.23	$241.25	$241.20
Purchase #4	$109.40	7.748%	$117.8763	$117.88	$117.90	$117.90
Purchase #5	$13.47	4.136%	$14.0271	$14.03	$14.05	$14.00
Purchase #6	$240.92	8.285%	$260.8802	$260.88	$260.90	$260.90
Purchase #7	$75.86	8.458%	$82.2762	$82.28	$82.30	$82.30
7 purchase totals =	$895.66		$968.8109	$968.83	$968.90	$968.90