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	$40.49	11.801%	$45.2682	$45.27	$45.25	$45.30
Purchase #2	$58.85	13.442%	$66.7606	$66.76	$66.75	$66.80
Purchase #3	$224.39	4.196%	$233.8054	$233.81	$233.80	$233.80
Purchase #4	$170.61	9.840%	$187.398	$187.40	$187.40	$187.40
Purchase #5	$187.58	4.669%	$196.3381	$196.34	$196.35	$196.30
Purchase #6	$81.80	3.272%	$84.4765	$84.48	$84.50	$84.50
Purchase #7	$16.31	11.362%	$18.1631	$18.16	$18.15	$18.20
7 purchase totals =	$780.03		$832.2099	$832.22	$832.20	$832.30