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	$17.86	3.665%	$18.5146	$18.51	$18.50	$18.50
Purchase #2	$71.73	13.353%	$81.3081	$81.31	$81.30	$81.30
Purchase #3	$113.36	3.541%	$117.3741	$117.37	$117.35	$117.40
Purchase #4	$127.94	3.370%	$132.2516	$132.25	$132.25	$132.30
Purchase #5	$139.61	9.151%	$152.3857	$152.39	$152.40	$152.40
Purchase #6	$164.73	9.824%	$180.9131	$180.91	$180.90	$180.90
Purchase #7	$127.71	3.663%	$132.388	$132.39	$132.40	$132.40
7 purchase totals =	$762.94		$815.1352	$815.13	$815.10	$815.20