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	$129.36	11.788%	$144.609	$144.61	$144.60	$144.60
Purchase #2	$203.97	5.439%	$215.0639	$215.06	$215.05	$215.10
Purchase #3	$219.75	7.141%	$235.4423	$235.44	$235.45	$235.40
Purchase #4	$32.40	12.669%	$36.5048	$36.50	$36.50	$36.50
Purchase #5	$64.42	4.808%	$67.5173	$67.52	$67.50	$67.50
Purchase #6	$11.46	9.638%	$12.5645	$12.56	$12.55	$12.60
Purchase #7	$30.71	3.830%	$31.8862	$31.89	$31.90	$31.90
7 purchase totals =	$692.07		$743.5880	$743.58	$743.55	$743.60