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	$115.88	10.853%	$128.4565	$128.46	$128.45	$128.50
Purchase #2	$167.85	12.679%	$189.1317	$189.13	$189.15	$189.10
Purchase #3	$150.90	6.246%	$160.3252	$160.33	$160.35	$160.30
Purchase #4	$202.36	13.216%	$229.1039	$229.10	$229.10	$229.10
Purchase #5	$120.75	13.570%	$137.1358	$137.14	$137.15	$137.10
Purchase #6	$139.69	4.224%	$145.5905	$145.59	$145.60	$145.60
Purchase #7	$80.40	3.125%	$82.9125	$82.91	$82.90	$82.90
7 purchase totals =	$977.83		$1,072.6561	$1,072.66	$1,072.70	$1,072.60