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	$74.59	11.382%	$83.0798	$83.08	$83.10	$83.10
Purchase #2	$99.85	3.569%	$103.4136	$103.41	$103.40	$103.40
Purchase #3	$141.76	9.213%	$154.8203	$154.82	$154.80	$154.80
Purchase #4	$221.49	8.730%	$240.8261	$240.83	$240.85	$240.80
Purchase #5	$219.45	6.314%	$233.3061	$233.31	$233.30	$233.30
Purchase #6	$101.39	13.440%	$115.0168	$115.02	$115.00	$115.00
Purchase #7	$149.32	12.709%	$168.2971	$168.30	$168.30	$168.30
7 purchase totals =	$1,007.85		$1,098.7598	$1,098.77	$1,098.75	$1,098.70