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	$23.31	7.874%	$25.1454	$25.15	$25.15	$25.10
Purchase #2	$38.31	6.123%	$40.6557	$40.66	$40.65	$40.70
Purchase #3	$50.27	6.649%	$53.6125	$53.61	$53.60	$53.60
Purchase #4	$108.87	13.478%	$123.5435	$123.54	$123.55	$123.50
Purchase #5	$47.31	12.586%	$53.2644	$53.26	$53.25	$53.30
Purchase #6	$185.85	7.400%	$199.6029	$199.60	$199.60	$199.60
Purchase #7	$166.91	12.361%	$187.5417	$187.54	$187.55	$187.50
7 purchase totals =	$620.83		$683.3661	$683.36	$683.35	$683.30