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	$123.59	11.381%	$137.6558	$137.66	$137.65	$137.70
Purchase #2	$31.42	5.491%	$33.1453	$33.15	$33.15	$33.10
Purchase #3	$87.62	10.653%	$96.9542	$96.95	$96.95	$97.00
Purchase #4	$51.77	13.470%	$58.7434	$58.74	$58.75	$58.70
Purchase #5	$142.89	12.337%	$160.5183	$160.52	$160.50	$160.50
Purchase #6	$47.86	8.522%	$51.9386	$51.94	$51.95	$51.90
Purchase #7	$80.36	11.778%	$89.8248	$89.82	$89.80	$89.80
7 purchase totals =	$565.51		$628.7804	$628.78	$628.75	$628.70