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	$105.28	4.236%	$109.7397	$109.74	$109.75	$109.70
Purchase #2	$57.72	8.822%	$62.8121	$62.81	$62.80	$62.80
Purchase #3	$188.45	5.210%	$198.2682	$198.27	$198.25	$198.30
Purchase #4	$25.42	10.138%	$27.9971	$28.00	$28.00	$28.00
Purchase #5	$105.84	13.768%	$120.4121	$120.41	$120.40	$120.40
Purchase #6	$127.61	12.323%	$143.3354	$143.34	$143.35	$143.30
Purchase #7	$110.31	5.691%	$116.5877	$116.59	$116.60	$116.60
7 purchase totals =	$720.63		$779.1523	$779.16	$779.15	$779.10