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	$124.43	12.273%	$139.7013	$139.70	$139.70	$139.70
Purchase #2	$211.59	3.794%	$219.6177	$219.62	$219.60	$219.60
Purchase #3	$61.44	5.553%	$64.8518	$64.85	$64.85	$64.90
Purchase #4	$132.74	9.860%	$145.8282	$145.83	$145.85	$145.80
Purchase #5	$98.38	5.800%	$104.086	$104.09	$104.10	$104.10
Purchase #6	$24.40	11.222%	$27.1382	$27.14	$27.15	$27.10
Purchase #7	$80.47	10.853%	$89.2034	$89.20	$89.20	$89.20
7 purchase totals =	$733.45		$790.4266	$790.43	$790.45	$790.40