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	$185.67	5.853%	$196.5373	$196.54	$196.55	$196.50
Purchase #2	$75.56	9.304%	$82.5901	$82.59	$82.60	$82.60
Purchase #3	$106.41	3.193%	$109.8077	$109.81	$109.80	$109.80
Purchase #4	$222.49	8.245%	$240.8343	$240.83	$240.85	$240.80
Purchase #5	$62.50	6.385%	$66.4906	$66.49	$66.50	$66.50
Purchase #6	$53.87	7.482%	$57.9006	$57.90	$57.90	$57.90
Purchase #7	$227.49	8.204%	$246.1533	$246.15	$246.15	$246.20
7 purchase totals =	$933.99		$1,000.3139	$1,000.31	$1,000.35	$1,000.30