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	$56.77	5.475%	$59.8782	$59.88	$59.90	$59.90
Purchase #2	$132.79	13.406%	$150.5918	$150.59	$150.60	$150.60
Purchase #3	$134.68	11.649%	$150.3689	$150.37	$150.35	$150.40
Purchase #4	$76.41	9.848%	$83.9349	$83.93	$83.95	$83.90
Purchase #5	$225.29	8.274%	$243.9305	$243.93	$243.95	$243.90
Purchase #6	$109.33	9.811%	$120.0564	$120.06	$120.05	$120.10
Purchase #7	$19.75	12.679%	$22.2541	$22.25	$22.25	$22.30
7 purchase totals =	$755.02		$831.0148	$831.01	$831.05	$831.10