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	$20.25	4.329%	$21.1266	$21.13	$21.15	$21.10
Purchase #2	$129.53	3.851%	$134.5182	$134.52	$134.50	$134.50
Purchase #3	$164.78	5.668%	$174.1197	$174.12	$174.10	$174.10
Purchase #4	$104.62	11.326%	$116.4693	$116.47	$116.45	$116.50
Purchase #5	$92.57	7.792%	$99.7831	$99.78	$99.80	$99.80
Purchase #6	$64.87	11.699%	$72.4591	$72.46	$72.45	$72.50
Purchase #7	$29.88	6.853%	$31.9277	$31.93	$31.95	$31.90
7 purchase totals =	$606.50		$650.4037	$650.41	$650.40	$650.40