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	$79.72	12.358%	$89.5718	$89.57	$89.55	$89.60
Purchase #2	$170.33	4.724%	$178.3764	$178.38	$178.40	$178.40
Purchase #3	$187.25	3.486%	$193.7775	$193.78	$193.80	$193.80
Purchase #4	$129.72	11.420%	$144.534	$144.53	$144.55	$144.50
Purchase #5	$43.63	9.182%	$47.6361	$47.64	$47.65	$47.60
Purchase #6	$20.34	12.158%	$22.8129	$22.81	$22.80	$22.80
Purchase #7	$131.80	8.194%	$142.5997	$142.60	$142.60	$142.60
7 purchase totals =	$762.79		$819.3084	$819.31	$819.35	$819.30