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	$126.76	13.747%	$144.1857	$144.19	$144.20	$144.20
Purchase #2	$101.25	11.510%	$112.9039	$112.90	$112.90	$112.90
Purchase #3	$28.38	3.494%	$29.3716	$29.37	$29.35	$29.40
Purchase #4	$80.86	3.709%	$83.8591	$83.86	$83.85	$83.90
Purchase #5	$168.41	5.391%	$177.489	$177.49	$177.50	$177.50
Purchase #6	$165.88	11.727%	$185.3327	$185.33	$185.35	$185.30
Purchase #7	$12.83	12.745%	$14.4652	$14.47	$14.45	$14.50
7 purchase totals =	$684.37		$747.6072	$747.61	$747.60	$747.70