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	$99.27	4.627%	$103.8632	$103.86	$103.85	$103.90
Purchase #2	$186.84	10.407%	$206.2844	$206.28	$206.30	$206.30
Purchase #3	$224.74	7.438%	$241.4562	$241.46	$241.45	$241.50
Purchase #4	$47.91	7.465%	$51.4865	$51.49	$51.50	$51.50
Purchase #5	$56.52	5.549%	$59.6563	$59.66	$59.65	$59.70
Purchase #6	$34.93	9.679%	$38.3109	$38.31	$38.30	$38.30
Purchase #7	$211.75	4.159%	$220.5567	$220.56	$220.55	$220.60
7 purchase totals =	$861.96		$921.6142	$921.62	$921.60	$921.80