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	$26.94	7.272%	$28.8991	$28.90	$28.90	$28.90
Purchase #2	$19.71	10.649%	$21.8089	$21.81	$21.80	$21.80
Purchase #3	$24.38	13.742%	$27.7303	$27.73	$27.75	$27.70
Purchase #4	$48.71	3.597%	$50.4621	$50.46	$50.45	$50.50
Purchase #5	$115.59	4.262%	$120.5164	$120.52	$120.50	$120.50
Purchase #6	$172.93	3.779%	$179.465	$179.47	$179.45	$179.50
Purchase #7	$68.59	13.790%	$78.0486	$78.05	$78.05	$78.00
7 purchase totals =	$476.85		$506.9304	$506.94	$506.90	$506.90