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	$112.51	13.247%	$127.4142	$127.41	$127.40	$127.40
Purchase #2	$189.50	10.571%	$209.532	$209.53	$209.55	$209.50
Purchase #3	$203.70	7.719%	$219.4236	$219.42	$219.40	$219.40
Purchase #4	$70.61	11.785%	$78.9314	$78.93	$78.95	$78.90
Purchase #5	$33.30	7.743%	$35.8784	$35.88	$35.90	$35.90
Purchase #6	$17.36	13.776%	$19.7515	$19.75	$19.75	$19.80
Purchase #7	$194.45	7.440%	$208.9171	$208.92	$208.90	$208.90
7 purchase totals =	$821.43		$899.8482	$899.84	$899.85	$899.80