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	$132.88	4.370%	$138.6869	$138.69	$138.70	$138.70
Purchase #2	$232.93	9.532%	$255.1329	$255.13	$255.15	$255.10
Purchase #3	$131.86	7.450%	$141.6836	$141.68	$141.70	$141.70
Purchase #4	$196.62	9.587%	$215.47	$215.47	$215.45	$215.50
Purchase #5	$49.69	4.496%	$51.9241	$51.92	$51.90	$51.90
Purchase #6	$46.73	13.797%	$53.1773	$53.18	$53.20	$53.20
Purchase #7	$156.45	4.842%	$164.0253	$164.03	$164.05	$164.00
7 purchase totals =	$947.16		$1,020.1001	$1,020.10	$1,020.15	$1,020.10