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	$35.70	3.502%	$36.9502	$36.95	$36.95	$37.00
Purchase #2	$123.73	13.175%	$140.0314	$140.03	$140.05	$140.00
Purchase #3	$152.45	9.269%	$166.5806	$166.58	$166.60	$166.60
Purchase #4	$141.43	7.822%	$152.4927	$152.49	$152.50	$152.50
Purchase #5	$80.40	5.792%	$85.0568	$85.06	$85.05	$85.10
Purchase #6	$249.55	6.567%	$265.9379	$265.94	$265.95	$265.90
Purchase #7	$107.91	4.283%	$112.5318	$112.53	$112.55	$112.50
7 purchase totals =	$891.17		$959.5814	$959.58	$959.65	$959.60