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	$158.53	6.233%	$168.4112	$168.41	$168.40	$168.40
Purchase #2	$81.26	4.142%	$84.6258	$84.63	$84.65	$84.60
Purchase #3	$59.41	11.819%	$66.4317	$66.43	$66.45	$66.40
Purchase #4	$215.58	10.116%	$237.3881	$237.39	$237.40	$237.40
Purchase #5	$134.55	12.704%	$151.6432	$151.64	$151.65	$151.60
Purchase #6	$80.91	10.486%	$89.3942	$89.39	$89.40	$89.40
Purchase #7	$54.50	11.193%	$60.6002	$60.60	$60.60	$60.60
7 purchase totals =	$784.74		$858.4944	$858.49	$858.55	$858.40