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	$82.65	9.846%	$90.7877	$90.79	$90.80	$90.80
Purchase #2	$201.97	13.338%	$228.9088	$228.91	$228.90	$228.90
Purchase #3	$138.51	3.870%	$143.8703	$143.87	$143.85	$143.90
Purchase #4	$34.78	7.751%	$37.4758	$37.48	$37.50	$37.50
Purchase #5	$112.48	3.856%	$116.8172	$116.82	$116.80	$116.80
Purchase #6	$211.90	3.432%	$219.1724	$219.17	$219.15	$219.20
Purchase #7	$143.95	8.368%	$155.9957	$156.00	$156.00	$156.00
7 purchase totals =	$926.24		$993.0279	$993.04	$993.00	$993.10