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	$38.81	4.726%	$40.6442	$40.64	$40.65	$40.60
Purchase #2	$240.60	12.794%	$271.3824	$271.38	$271.40	$271.40
Purchase #3	$139.54	12.464%	$156.9323	$156.93	$156.95	$156.90
Purchase #4	$24.73	3.233%	$25.5295	$25.53	$25.55	$25.50
Purchase #5	$12.92	4.568%	$13.5102	$13.51	$13.50	$13.50
Purchase #6	$131.94	7.305%	$141.5782	$141.58	$141.60	$141.60
Purchase #7	$51.71	9.590%	$56.669	$56.67	$56.65	$56.70
7 purchase totals =	$640.25		$706.2458	$706.24	$706.30	$706.20