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	$95.82	4.706%	$100.3293	$100.33	$100.35	$100.30
Purchase #2	$161.49	7.784%	$174.0604	$174.06	$174.05	$174.10
Purchase #3	$136.77	10.279%	$150.8286	$150.83	$150.85	$150.80
Purchase #4	$43.49	6.725%	$46.4147	$46.41	$46.40	$46.40
Purchase #5	$78.48	13.601%	$89.1541	$89.15	$89.15	$89.20
Purchase #6	$89.98	9.152%	$98.215	$98.22	$98.20	$98.20
Purchase #7	$141.50	11.236%	$157.3989	$157.40	$157.40	$157.40
7 purchase totals =	$747.53		$816.4010	$816.40	$816.40	$816.40