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	$38.96	4.636%	$40.7662	$40.77	$40.75	$40.80
Purchase #2	$154.29	8.858%	$167.957	$167.96	$167.95	$168.00
Purchase #3	$94.55	9.842%	$103.8556	$103.86	$103.85	$103.90
Purchase #4	$86.49	9.732%	$94.9072	$94.91	$94.90	$94.90
Purchase #5	$11.60	10.192%	$12.7823	$12.78	$12.80	$12.80
Purchase #6	$207.72	8.281%	$224.9213	$224.92	$224.90	$224.90
Purchase #7	$21.30	13.562%	$24.1887	$24.19	$24.20	$24.20
7 purchase totals =	$614.91		$669.3783	$669.39	$669.35	$669.50