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	$240.79	5.663%	$254.4259	$254.43	$254.45	$254.40
Purchase #2	$159.90	5.314%	$168.3971	$168.40	$168.40	$168.40
Purchase #3	$50.42	13.152%	$57.0512	$57.05	$57.05	$57.10
Purchase #4	$125.69	12.469%	$141.3623	$141.36	$141.35	$141.40
Purchase #5	$105.71	5.455%	$111.4765	$111.48	$111.50	$111.50
Purchase #6	$112.52	5.185%	$118.3542	$118.35	$118.35	$118.40
Purchase #7	$55.67	10.133%	$61.311	$61.31	$61.30	$61.30
7 purchase totals =	$850.70		$912.3782	$912.38	$912.40	$912.50