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	$50.28	7.593%	$54.0978	$54.10	$54.10	$54.10
Purchase #2	$19.27	6.176%	$20.4601	$20.46	$20.45	$20.50
Purchase #3	$176.82	9.843%	$194.2244	$194.22	$194.20	$194.20
Purchase #4	$78.27	5.867%	$82.8621	$82.86	$82.85	$82.90
Purchase #5	$30.25	4.243%	$31.5335	$31.53	$31.55	$31.50
Purchase #6	$62.39	10.579%	$68.9902	$68.99	$69.00	$69.00
Purchase #7	$165.40	12.689%	$186.3876	$186.39	$186.40	$186.40
7 purchase totals =	$582.68		$638.5557	$638.55	$638.55	$638.60