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	$17.55	5.274%	$18.4756	$18.48	$18.50	$18.50
Purchase #2	$178.27	6.210%	$189.3406	$189.34	$189.35	$189.30
Purchase #3	$63.99	13.107%	$72.3772	$72.38	$72.40	$72.40
Purchase #4	$126.85	12.309%	$142.464	$142.46	$142.45	$142.50
Purchase #5	$60.49	12.346%	$67.9581	$67.96	$67.95	$68.00
Purchase #6	$161.58	5.639%	$170.6915	$170.69	$170.70	$170.70
Purchase #7	$67.27	4.301%	$70.1633	$70.16	$70.15	$70.20
7 purchase totals =	$676.00		$731.4703	$731.47	$731.50	$731.60