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	$246.42	13.455%	$279.5758	$279.58	$279.60	$279.60
Purchase #2	$80.32	4.291%	$83.7665	$83.77	$83.75	$83.80
Purchase #3	$197.60	5.465%	$208.3988	$208.40	$208.40	$208.40
Purchase #4	$69.81	4.661%	$73.0638	$73.06	$73.05	$73.10
Purchase #5	$116.67	12.552%	$131.3144	$131.31	$131.30	$131.30
Purchase #6	$19.36	5.256%	$20.3776	$20.38	$20.40	$20.40
Purchase #7	$34.33	12.399%	$38.5866	$38.59	$38.60	$38.60
7 purchase totals =	$764.51		$835.0835	$835.09	$835.10	$835.20