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	$19.26	4.377%	$20.103	$20.10	$20.10	$20.10
Purchase #2	$83.97	13.784%	$95.5444	$95.54	$95.55	$95.50
Purchase #3	$10.93	8.834%	$11.8956	$11.90	$11.90	$11.90
Purchase #4	$97.98	11.699%	$109.4427	$109.44	$109.45	$109.40
Purchase #5	$68.98	3.598%	$71.4619	$71.46	$71.45	$71.50
Purchase #6	$228.92	4.601%	$239.4526	$239.45	$239.45	$239.50
Purchase #7	$111.80	6.863%	$119.4728	$119.47	$119.45	$119.50
7 purchase totals =	$621.84		$667.3730	$667.36	$667.35	$667.40