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	$64.43	6.163%	$68.4008	$68.40	$68.40	$68.40
Purchase #2	$40.38	13.819%	$45.9601	$45.96	$45.95	$46.00
Purchase #3	$84.63	6.420%	$90.0632	$90.06	$90.05	$90.10
Purchase #4	$55.47	9.374%	$60.6698	$60.67	$60.65	$60.70
Purchase #5	$105.61	5.746%	$111.6784	$111.68	$111.70	$111.70
Purchase #6	$108.26	8.414%	$117.369	$117.37	$117.35	$117.40
Purchase #7	$52.95	11.497%	$59.0377	$59.04	$59.05	$59.00
7 purchase totals =	$511.73		$553.1790	$553.18	$553.15	$553.30