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	$130.57	10.320%	$144.0448	$144.04	$144.05	$144.00
Purchase #2	$55.28	12.333%	$62.0977	$62.10	$62.10	$62.10
Purchase #3	$176.50	12.492%	$198.5484	$198.55	$198.55	$198.50
Purchase #4	$135.39	11.451%	$150.8935	$150.89	$150.90	$150.90
Purchase #5	$88.94	3.357%	$91.9257	$91.93	$91.95	$91.90
Purchase #6	$50.78	5.767%	$53.7085	$53.71	$53.70	$53.70
Purchase #7	$81.39	8.672%	$88.4481	$88.45	$88.45	$88.40
7 purchase totals =	$718.85		$789.6667	$789.67	$789.70	$789.50