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	$90.69	12.108%	$101.6707	$101.67	$101.65	$101.70
Purchase #2	$124.84	12.868%	$140.9044	$140.90	$140.90	$140.90
Purchase #3	$116.44	6.432%	$123.9294	$123.93	$123.95	$123.90
Purchase #4	$127.32	9.158%	$138.98	$138.98	$139.00	$139.00
Purchase #5	$81.98	10.211%	$90.351	$90.35	$90.35	$90.40
Purchase #6	$246.97	6.174%	$262.2179	$262.22	$262.20	$262.20
Purchase #7	$241.81	4.871%	$253.5886	$253.59	$253.60	$253.60
7 purchase totals =	$1,030.05		$1,111.6420	$1,111.64	$1,111.65	$1,111.70