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	$27.87	5.832%	$29.4954	$29.50	$29.50	$29.50
Purchase #2	$231.31	10.630%	$255.8983	$255.90	$255.90	$255.90
Purchase #3	$53.85	9.530%	$58.9819	$58.98	$59.00	$59.00
Purchase #4	$203.42	13.764%	$231.4187	$231.42	$231.40	$231.40
Purchase #5	$188.78	10.780%	$209.1305	$209.13	$209.15	$209.10
Purchase #6	$49.69	4.280%	$51.8167	$51.82	$51.80	$51.80
Purchase #7	$176.64	3.711%	$183.1951	$183.20	$183.20	$183.20
7 purchase totals =	$931.56		$1,019.9366	$1,019.95	$1,019.95	$1,019.90