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	$186.57	11.741%	$208.4752	$208.48	$208.50	$208.50
Purchase #2	$48.80	3.295%	$50.408	$50.41	$50.40	$50.40
Purchase #3	$164.94	4.179%	$171.8328	$171.83	$171.85	$171.80
Purchase #4	$24.39	4.749%	$25.5483	$25.55	$25.55	$25.50
Purchase #5	$82.78	6.816%	$88.4223	$88.42	$88.40	$88.40
Purchase #6	$111.32	3.274%	$114.9646	$114.96	$114.95	$115.00
Purchase #7	$23.38	5.220%	$24.6004	$24.60	$24.60	$24.60
7 purchase totals =	$642.18		$684.2516	$684.25	$684.25	$684.20