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	$39.86	6.490%	$42.4469	$42.45	$42.45	$42.40
Purchase #2	$133.59	7.571%	$143.7041	$143.70	$143.70	$143.70
Purchase #3	$190.34	13.459%	$215.9579	$215.96	$215.95	$216.00
Purchase #4	$69.71	12.683%	$78.5513	$78.55	$78.55	$78.60
Purchase #5	$99.58	7.773%	$107.3204	$107.32	$107.30	$107.30
Purchase #6	$133.64	10.455%	$147.6121	$147.61	$147.60	$147.60
Purchase #7	$135.52	4.778%	$141.9951	$142.00	$142.00	$142.00
7 purchase totals =	$802.24		$877.5878	$877.59	$877.55	$877.60