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	$147.88	9.624%	$162.112	$162.11	$162.10	$162.10
Purchase #2	$139.57	12.203%	$156.6017	$156.60	$156.60	$156.60
Purchase #3	$103.35	6.226%	$109.7846	$109.78	$109.80	$109.80
Purchase #4	$71.96	12.187%	$80.7298	$80.73	$80.75	$80.70
Purchase #5	$8.71	11.446%	$9.7069	$9.71	$9.70	$9.70
Purchase #6	$43.60	10.365%	$48.1191	$48.12	$48.10	$48.10
Purchase #7	$69.56	4.556%	$72.7292	$72.73	$72.75	$72.70
7 purchase totals =	$584.63		$639.7833	$639.78	$639.80	$639.70