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	$50.65	4.466%	$52.912	$52.91	$52.90	$52.90
Purchase #2	$196.69	10.582%	$217.5037	$217.50	$217.50	$217.50
Purchase #3	$120.71	9.708%	$132.4285	$132.43	$132.45	$132.40
Purchase #4	$72.89	11.610%	$81.3525	$81.35	$81.35	$81.40
Purchase #5	$76.57	5.536%	$80.8089	$80.81	$80.80	$80.80
Purchase #6	$27.48	7.278%	$29.48	$29.48	$29.50	$29.50
Purchase #7	$184.83	7.647%	$198.964	$198.96	$198.95	$199.00
7 purchase totals =	$729.82		$793.4496	$793.44	$793.45	$793.50