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	$177.53	4.124%	$184.8513	$184.85	$184.85	$184.90
Purchase #2	$118.29	4.439%	$123.5409	$123.54	$123.55	$123.50
Purchase #3	$225.30	4.107%	$234.5531	$234.55	$234.55	$234.60
Purchase #4	$57.27	9.120%	$62.493	$62.49	$62.50	$62.50
Purchase #5	$40.90	10.782%	$45.3098	$45.31	$45.30	$45.30
Purchase #6	$19.98	8.765%	$21.7312	$21.73	$21.75	$21.70
Purchase #7	$137.84	5.813%	$145.8526	$145.85	$145.85	$145.90
7 purchase totals =	$777.11		$818.3319	$818.32	$818.35	$818.40