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	$71.25	11.321%	$79.3162	$79.32	$79.30	$79.30
Purchase #2	$117.33	11.680%	$131.0341	$131.03	$131.05	$131.00
Purchase #3	$18.72	3.176%	$19.3145	$19.31	$19.30	$19.30
Purchase #4	$184.29	3.463%	$190.672	$190.67	$190.65	$190.70
Purchase #5	$190.96	9.410%	$208.9293	$208.93	$208.95	$208.90
Purchase #6	$32.28	6.691%	$34.4399	$34.44	$34.45	$34.40
Purchase #7	$196.93	13.305%	$223.1315	$223.13	$223.15	$223.10
7 purchase totals =	$811.76		$886.8375	$886.83	$886.85	$886.70