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	$167.62	6.686%	$178.8271	$178.83	$178.85	$178.80
Purchase #2	$237.80	5.239%	$250.2583	$250.26	$250.25	$250.30
Purchase #3	$75.34	9.293%	$82.3413	$82.34	$82.35	$82.30
Purchase #4	$112.69	10.556%	$124.5856	$124.59	$124.60	$124.60
Purchase #5	$128.90	12.756%	$145.3425	$145.34	$145.35	$145.30
Purchase #6	$230.41	10.852%	$255.4141	$255.41	$255.40	$255.40
Purchase #7	$45.33	4.107%	$47.1917	$47.19	$47.20	$47.20
7 purchase totals =	$998.09		$1,083.9606	$1,083.96	$1,084.00	$1,083.90