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	$32.35	3.549%	$33.4981	$33.50	$33.50	$33.50
Purchase #2	$40.46	9.722%	$44.3935	$44.39	$44.40	$44.40
Purchase #3	$216.55	5.158%	$227.7196	$227.72	$227.70	$227.70
Purchase #4	$13.52	13.772%	$15.382	$15.38	$15.40	$15.40
Purchase #5	$202.61	6.752%	$216.2902	$216.29	$216.30	$216.30
Purchase #6	$213.25	4.476%	$222.7951	$222.80	$222.80	$222.80
Purchase #7	$50.35	7.840%	$54.2974	$54.30	$54.30	$54.30
7 purchase totals =	$769.09		$814.3759	$814.38	$814.40	$814.40