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	$25.95	13.267%	$29.3928	$29.39	$29.40	$29.40
Purchase #2	$182.97	7.384%	$196.4805	$196.48	$196.50	$196.50
Purchase #3	$191.59	3.638%	$198.56	$198.56	$198.55	$198.60
Purchase #4	$30.78	3.788%	$31.9459	$31.95	$31.95	$31.90
Purchase #5	$202.80	9.235%	$221.5286	$221.53	$221.55	$221.50
Purchase #6	$222.69	5.764%	$235.5259	$235.53	$235.55	$235.50
Purchase #7	$16.72	6.351%	$17.7819	$17.78	$17.80	$17.80
7 purchase totals =	$873.50		$931.2156	$931.22	$931.30	$931.20