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	$187.87	13.586%	$213.394	$213.39	$213.40	$213.40
Purchase #2	$23.72	3.522%	$24.5554	$24.56	$24.55	$24.60
Purchase #3	$139.29	6.638%	$148.5361	$148.54	$148.55	$148.50
Purchase #4	$145.49	4.589%	$152.1665	$152.17	$152.15	$152.20
Purchase #5	$197.91	12.596%	$222.8387	$222.84	$222.85	$222.80
Purchase #6	$66.70	8.550%	$72.4029	$72.40	$72.40	$72.40
Purchase #7	$104.47	10.336%	$115.268	$115.27	$115.25	$115.30
7 purchase totals =	$865.45		$949.1616	$949.17	$949.15	$949.20