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	$210.98	4.567%	$220.6155	$220.62	$220.60	$220.60
Purchase #2	$115.66	11.414%	$128.8614	$128.86	$128.85	$128.90
Purchase #3	$181.35	13.230%	$205.3426	$205.34	$205.35	$205.30
Purchase #4	$74.80	11.230%	$83.2	$83.20	$83.20	$83.20
Purchase #5	$84.72	6.829%	$90.5055	$90.51	$90.50	$90.50
Purchase #6	$123.83	11.246%	$137.7559	$137.76	$137.75	$137.80
Purchase #7	$17.47	5.473%	$18.4261	$18.43	$18.45	$18.40
7 purchase totals =	$808.81		$884.7070	$884.72	$884.70	$884.70