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	$122.48	6.674%	$130.6543	$130.65	$130.65	$130.70
Purchase #2	$200.50	13.439%	$227.4452	$227.45	$227.45	$227.40
Purchase #3	$147.81	13.748%	$168.1309	$168.13	$168.15	$168.10
Purchase #4	$209.41	8.158%	$226.4937	$226.49	$226.50	$226.50
Purchase #5	$77.37	6.750%	$82.5925	$82.59	$82.60	$82.60
Purchase #6	$17.76	7.601%	$19.1099	$19.11	$19.10	$19.10
Purchase #7	$102.39	13.776%	$116.4952	$116.50	$116.50	$116.50
7 purchase totals =	$877.72		$970.9217	$970.92	$970.95	$970.90