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	$22.32	9.267%	$24.3884	$24.39	$24.40	$24.40
Purchase #2	$73.88	11.547%	$82.4109	$82.41	$82.40	$82.40
Purchase #3	$246.51	5.223%	$259.3852	$259.39	$259.40	$259.40
Purchase #4	$250.46	7.416%	$269.0341	$269.03	$269.05	$269.00
Purchase #5	$205.78	11.538%	$229.5229	$229.52	$229.50	$229.50
Purchase #6	$19.71	13.703%	$22.4109	$22.41	$22.40	$22.40
Purchase #7	$52.38	7.527%	$56.3226	$56.32	$56.30	$56.30
7 purchase totals =	$871.04		$943.4750	$943.47	$943.45	$943.40