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	$35.52	11.480%	$39.5977	$39.60	$39.60	$39.60
Purchase #2	$11.83	6.429%	$12.5906	$12.59	$12.60	$12.60
Purchase #3	$233.69	12.319%	$262.4783	$262.48	$262.50	$262.50
Purchase #4	$108.49	6.291%	$115.3151	$115.32	$115.30	$115.30
Purchase #5	$98.94	10.318%	$109.1486	$109.15	$109.15	$109.10
Purchase #6	$209.76	13.532%	$238.1447	$238.14	$238.15	$238.10
Purchase #7	$121.26	6.339%	$128.9467	$128.95	$128.95	$128.90
7 purchase totals =	$819.49		$906.2217	$906.23	$906.25	$906.10