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	$250.84	12.681%	$282.649	$282.65	$282.65	$282.60
Purchase #2	$179.35	4.485%	$187.3938	$187.39	$187.40	$187.40
Purchase #3	$24.29	5.377%	$25.5961	$25.60	$25.60	$25.60
Purchase #4	$199.30	8.190%	$215.6227	$215.62	$215.60	$215.60
Purchase #5	$55.76	6.542%	$59.4078	$59.41	$59.40	$59.40
Purchase #6	$105.29	9.488%	$115.2799	$115.28	$115.30	$115.30
Purchase #7	$145.74	5.288%	$153.4467	$153.45	$153.45	$153.40
7 purchase totals =	$960.57		$1,039.3960	$1,039.40	$1,039.40	$1,039.30