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	$132.45	11.131%	$147.193	$147.19	$147.20	$147.20
Purchase #2	$143.94	4.853%	$150.9254	$150.93	$150.95	$150.90
Purchase #3	$97.72	4.287%	$101.9093	$101.91	$101.90	$101.90
Purchase #4	$9.46	10.292%	$10.4336	$10.43	$10.45	$10.40
Purchase #5	$32.86	5.310%	$34.6049	$34.60	$34.60	$34.60
Purchase #6	$212.81	12.280%	$238.9431	$238.94	$238.95	$238.90
Purchase #7	$18.46	13.796%	$21.0067	$21.01	$21.00	$21.00
7 purchase totals =	$647.70		$705.0160	$705.01	$705.05	$704.90