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	$11.59	7.225%	$12.4274	$12.43	$12.45	$12.40
Purchase #2	$9.70	13.467%	$11.0063	$11.01	$11.00	$11.00
Purchase #3	$175.69	5.741%	$185.7764	$185.78	$185.80	$185.80
Purchase #4	$109.61	10.357%	$120.9623	$120.96	$120.95	$121.00
Purchase #5	$37.68	10.537%	$41.6503	$41.65	$41.65	$41.70
Purchase #6	$161.78	9.698%	$177.4694	$177.47	$177.45	$177.50
Purchase #7	$40.36	4.123%	$42.024	$42.02	$42.00	$42.00
7 purchase totals =	$546.41		$591.3161	$591.32	$591.30	$591.40