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	$13.65	11.586%	$15.2315	$15.23	$15.25	$15.20
Purchase #2	$65.73	9.632%	$72.0611	$72.06	$72.05	$72.10
Purchase #3	$197.79	13.544%	$224.5787	$224.58	$224.60	$224.60
Purchase #4	$107.79	3.289%	$111.3352	$111.34	$111.35	$111.30
Purchase #5	$139.96	13.152%	$158.3675	$158.37	$158.35	$158.40
Purchase #6	$54.28	9.836%	$59.619	$59.62	$59.60	$59.60
Purchase #7	$232.50	12.833%	$262.3367	$262.34	$262.35	$262.30
7 purchase totals =	$811.70		$903.5297	$903.54	$903.55	$903.50