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	$171.51	10.626%	$189.7347	$189.73	$189.75	$189.70
Purchase #2	$98.32	13.302%	$111.3985	$111.40	$111.40	$111.40
Purchase #3	$97.41	6.336%	$103.5819	$103.58	$103.60	$103.60
Purchase #4	$158.45	4.525%	$165.6199	$165.62	$165.60	$165.60
Purchase #5	$137.61	4.397%	$143.6607	$143.66	$143.65	$143.70
Purchase #6	$128.91	6.468%	$137.2479	$137.25	$137.25	$137.20
Purchase #7	$200.34	9.144%	$218.6591	$218.66	$218.65	$218.70
7 purchase totals =	$992.55		$1,069.9027	$1,069.90	$1,069.90	$1,069.90