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	$22.25	9.766%	$24.4229	$24.42	$24.40	$24.40
Purchase #2	$35.73	3.684%	$37.0463	$37.05	$37.05	$37.00
Purchase #3	$191.73	8.624%	$208.2648	$208.26	$208.25	$208.30
Purchase #4	$196.96	13.366%	$223.2857	$223.29	$223.30	$223.30
Purchase #5	$151.48	8.341%	$164.1149	$164.11	$164.10	$164.10
Purchase #6	$120.76	10.838%	$133.848	$133.85	$133.85	$133.80
Purchase #7	$89.58	12.547%	$100.8196	$100.82	$100.80	$100.80
7 purchase totals =	$808.49		$891.8022	$891.80	$891.75	$891.70