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	$200.81	4.376%	$209.5974	$209.60	$209.60	$209.60
Purchase #2	$183.47	7.602%	$197.4174	$197.42	$197.40	$197.40
Purchase #3	$125.90	4.599%	$131.6901	$131.69	$131.70	$131.70
Purchase #4	$162.25	11.467%	$180.8552	$180.86	$180.85	$180.90
Purchase #5	$64.33	9.621%	$70.5192	$70.52	$70.50	$70.50
Purchase #6	$33.76	5.160%	$35.502	$35.50	$35.50	$35.50
Purchase #7	$70.25	11.329%	$78.2086	$78.21	$78.20	$78.20
7 purchase totals =	$840.77		$903.7899	$903.80	$903.75	$903.80