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	$37.85	13.874%	$43.1013	$43.10	$43.10	$43.10
Purchase #2	$100.94	7.494%	$108.5044	$108.50	$108.50	$108.50
Purchase #3	$46.81	7.835%	$50.4776	$50.48	$50.50	$50.50
Purchase #4	$101.50	12.682%	$114.3722	$114.37	$114.35	$114.40
Purchase #5	$184.41	5.705%	$194.9306	$194.93	$194.95	$194.90
Purchase #6	$55.51	12.599%	$62.5037	$62.50	$62.50	$62.50
Purchase #7	$32.88	8.600%	$35.7077	$35.71	$35.70	$35.70
7 purchase totals =	$559.90		$609.5975	$609.59	$609.60	$609.60