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	$78.88	4.362%	$82.3207	$82.32	$82.30	$82.30
Purchase #2	$224.67	13.801%	$255.6767	$255.68	$255.70	$255.70
Purchase #3	$54.70	5.172%	$57.5291	$57.53	$57.55	$57.50
Purchase #4	$114.35	9.110%	$124.7673	$124.77	$124.75	$124.80
Purchase #5	$178.88	4.830%	$187.5199	$187.52	$187.50	$187.50
Purchase #6	$104.93	12.140%	$117.6685	$117.67	$117.65	$117.70
Purchase #7	$136.47	13.226%	$154.5195	$154.52	$154.50	$154.50
7 purchase totals =	$892.88		$980.0017	$980.01	$979.95	$980.00