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	$11.37	6.203%	$12.0753	$12.08	$12.10	$12.10
Purchase #2	$130.54	12.857%	$147.3235	$147.32	$147.30	$147.30
Purchase #3	$7.50	3.401%	$7.7551	$7.76	$7.75	$7.80
Purchase #4	$138.81	3.293%	$143.381	$143.38	$143.40	$143.40
Purchase #5	$151.36	4.732%	$158.5224	$158.52	$158.50	$158.50
Purchase #6	$5.64	12.849%	$6.3647	$6.36	$6.35	$6.40
Purchase #7	$164.73	13.810%	$187.4792	$187.48	$187.50	$187.50
7 purchase totals =	$609.95		$662.9012	$662.90	$662.90	$663.00