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	$90.33	11.597%	$100.8056	$100.81	$100.80	$100.80
Purchase #2	$6.34	11.840%	$7.0907	$7.09	$7.10	$7.10
Purchase #3	$156.47	10.421%	$172.7757	$172.78	$172.80	$172.80
Purchase #4	$77.92	3.263%	$80.4625	$80.46	$80.45	$80.50
Purchase #5	$100.55	13.784%	$114.4098	$114.41	$114.40	$114.40
Purchase #6	$168.76	7.705%	$181.763	$181.76	$181.75	$181.80
Purchase #7	$164.37	8.608%	$178.519	$178.52	$178.50	$178.50
7 purchase totals =	$764.74		$835.8263	$835.83	$835.80	$835.90