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	$15.61	3.243%	$16.1162	$16.12	$16.10	$16.10
Purchase #2	$160.86	11.335%	$179.0935	$179.09	$179.10	$179.10
Purchase #3	$24.63	13.349%	$27.9179	$27.92	$27.90	$27.90
Purchase #4	$182.46	8.398%	$197.783	$197.78	$197.80	$197.80
Purchase #5	$100.57	8.567%	$109.1858	$109.19	$109.20	$109.20
Purchase #6	$35.83	13.644%	$40.7186	$40.72	$40.70	$40.70
Purchase #7	$102.93	8.431%	$111.608	$111.61	$111.60	$111.60
7 purchase totals =	$622.89		$682.4230	$682.43	$682.40	$682.40