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	$173.91	9.176%	$189.868	$189.87	$189.85	$189.90
Purchase #2	$51.83	6.189%	$55.0378	$55.04	$55.05	$55.00
Purchase #3	$40.45	12.209%	$45.3885	$45.39	$45.40	$45.40
Purchase #4	$12.76	13.872%	$14.5301	$14.53	$14.55	$14.50
Purchase #5	$45.85	4.207%	$47.7789	$47.78	$47.80	$47.80
Purchase #6	$28.81	8.336%	$31.2116	$31.21	$31.20	$31.20
Purchase #7	$69.50	3.355%	$71.8317	$71.83	$71.85	$71.80
7 purchase totals =	$423.11		$455.6466	$455.65	$455.70	$455.60