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	$63.40	7.516%	$68.1651	$68.17	$68.15	$68.20
Purchase #2	$201.64	10.680%	$223.1752	$223.18	$223.20	$223.20
Purchase #3	$96.60	12.317%	$108.4982	$108.50	$108.50	$108.50
Purchase #4	$103.67	10.327%	$114.376	$114.38	$114.40	$114.40
Purchase #5	$43.96	4.513%	$45.9439	$45.94	$45.95	$45.90
Purchase #6	$76.70	7.208%	$82.2285	$82.23	$82.25	$82.20
Purchase #7	$35.70	13.616%	$40.5609	$40.56	$40.55	$40.60
7 purchase totals =	$621.67		$682.9478	$682.96	$683.00	$683.00