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	$131.96	10.738%	$146.1299	$146.13	$146.15	$146.10
Purchase #2	$135.83	11.792%	$151.8471	$151.85	$151.85	$151.80
Purchase #3	$153.39	9.662%	$168.2105	$168.21	$168.20	$168.20
Purchase #4	$88.81	3.666%	$92.0658	$92.07	$92.05	$92.10
Purchase #5	$250.28	5.291%	$263.5223	$263.52	$263.50	$263.50
Purchase #6	$16.56	8.424%	$17.955	$17.96	$17.95	$18.00
Purchase #7	$142.79	6.357%	$151.8672	$151.87	$151.85	$151.90
7 purchase totals =	$919.62		$991.5978	$991.61	$991.55	$991.60