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	$50.31	3.221%	$51.9305	$51.93	$51.95	$51.90
Purchase #2	$49.31	7.678%	$53.096	$53.10	$53.10	$53.10
Purchase #3	$38.62	10.200%	$42.5592	$42.56	$42.55	$42.60
Purchase #4	$97.78	8.576%	$106.1656	$106.17	$106.15	$106.20
Purchase #5	$110.52	7.338%	$118.63	$118.63	$118.65	$118.60
Purchase #6	$138.45	12.691%	$156.0207	$156.02	$156.00	$156.00
Purchase #7	$52.51	7.552%	$56.4756	$56.48	$56.50	$56.50
7 purchase totals =	$537.50		$584.8776	$584.89	$584.90	$584.90