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	$38.29	9.121%	$41.7824	$41.78	$41.80	$41.80
Purchase #2	$163.52	13.427%	$185.4758	$185.48	$185.50	$185.50
Purchase #3	$58.52	13.654%	$66.5103	$66.51	$66.50	$66.50
Purchase #4	$190.52	10.820%	$211.1343	$211.13	$211.15	$211.10
Purchase #5	$94.80	9.126%	$103.4514	$103.45	$103.45	$103.50
Purchase #6	$70.69	8.281%	$76.5438	$76.54	$76.55	$76.50
Purchase #7	$206.35	4.228%	$215.0745	$215.07	$215.05	$215.10
7 purchase totals =	$822.69		$899.9725	$899.96	$900.00	$900.00