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	$115.59	6.641%	$123.2663	$123.27	$123.25	$123.30
Purchase #2	$46.69	10.223%	$51.4631	$51.46	$51.45	$51.50
Purchase #3	$158.46	13.619%	$180.0407	$180.04	$180.05	$180.00
Purchase #4	$23.31	8.836%	$25.3697	$25.37	$25.35	$25.40
Purchase #5	$107.85	3.412%	$111.5298	$111.53	$111.55	$111.50
Purchase #6	$64.32	6.840%	$68.7195	$68.72	$68.70	$68.70
Purchase #7	$52.49	12.197%	$58.8922	$58.89	$58.90	$58.90
7 purchase totals =	$568.71		$619.2813	$619.28	$619.25	$619.30