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	$159.46	5.332%	$167.9624	$167.96	$167.95	$168.00
Purchase #2	$160.83	10.559%	$177.812	$177.81	$177.80	$177.80
Purchase #3	$22.92	11.377%	$25.5276	$25.53	$25.55	$25.50
Purchase #4	$114.59	3.725%	$118.8585	$118.86	$118.85	$118.90
Purchase #5	$122.55	7.144%	$131.305	$131.31	$131.30	$131.30
Purchase #6	$62.27	4.521%	$65.0852	$65.09	$65.10	$65.10
Purchase #7	$160.92	5.389%	$169.592	$169.59	$169.60	$169.60
7 purchase totals =	$803.54		$856.1427	$856.15	$856.15	$856.20