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	$75.39	4.486%	$78.772	$78.77	$78.75	$78.80
Purchase #2	$93.92	7.159%	$100.6437	$100.64	$100.65	$100.60
Purchase #3	$128.65	11.122%	$142.9585	$142.96	$142.95	$143.00
Purchase #4	$21.61	6.811%	$23.0819	$23.08	$23.10	$23.10
Purchase #5	$46.90	10.815%	$51.9722	$51.97	$51.95	$52.00
Purchase #6	$81.97	9.530%	$89.7817	$89.78	$89.80	$89.80
Purchase #7	$222.63	5.639%	$235.1841	$235.18	$235.20	$235.20
7 purchase totals =	$671.07		$722.3941	$722.38	$722.40	$722.50