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	$213.54	4.673%	$223.5187	$223.52	$223.50	$223.50
Purchase #2	$39.79	12.353%	$44.7053	$44.71	$44.70	$44.70
Purchase #3	$56.45	5.423%	$59.5113	$59.51	$59.50	$59.50
Purchase #4	$44.39	11.507%	$49.498	$49.50	$49.50	$49.50
Purchase #5	$186.63	6.610%	$198.9662	$198.97	$198.95	$199.00
Purchase #6	$41.26	5.647%	$43.59	$43.59	$43.60	$43.60
Purchase #7	$47.80	6.509%	$50.9113	$50.91	$50.90	$50.90
7 purchase totals =	$629.86		$670.7008	$670.71	$670.65	$670.70