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	$65.97	12.266%	$74.0619	$74.06	$74.05	$74.10
Purchase #2	$35.27	9.131%	$38.4905	$38.49	$38.50	$38.50
Purchase #3	$55.78	6.545%	$59.4308	$59.43	$59.45	$59.40
Purchase #4	$90.96	9.550%	$99.6467	$99.65	$99.65	$99.60
Purchase #5	$155.78	13.105%	$176.195	$176.20	$176.20	$176.20
Purchase #6	$157.62	6.718%	$168.2089	$168.21	$168.20	$168.20
Purchase #7	$61.36	9.568%	$67.2309	$67.23	$67.25	$67.20
7 purchase totals =	$622.74		$683.2647	$683.27	$683.30	$683.20