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	$12.29	4.486%	$12.8413	$12.84	$12.85	$12.80
Purchase #2	$19.61	3.278%	$20.2528	$20.25	$20.25	$20.30
Purchase #3	$94.86	9.333%	$103.7133	$103.71	$103.70	$103.70
Purchase #4	$20.36	5.411%	$21.4617	$21.46	$21.45	$21.50
Purchase #5	$11.90	10.653%	$13.1677	$13.17	$13.15	$13.20
Purchase #6	$131.78	4.362%	$137.5282	$137.53	$137.55	$137.50
Purchase #7	$134.74	6.445%	$143.424	$143.42	$143.40	$143.40
7 purchase totals =	$425.54		$452.3890	$452.38	$452.35	$452.40