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	$168.80	12.805%	$190.4148	$190.41	$190.40	$190.40
Purchase #2	$234.94	3.194%	$242.444	$242.44	$242.45	$242.40
Purchase #3	$132.37	5.353%	$139.4558	$139.46	$139.45	$139.50
Purchase #4	$65.74	4.483%	$68.6871	$68.69	$68.70	$68.70
Purchase #5	$82.38	9.603%	$90.291	$90.29	$90.30	$90.30
Purchase #6	$54.85	13.374%	$62.1856	$62.19	$62.20	$62.20
Purchase #7	$246.85	13.826%	$280.9795	$280.98	$281.00	$281.00
7 purchase totals =	$985.93		$1,074.4578	$1,074.46	$1,074.50	$1,074.50