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	$162.74	5.379%	$171.4938	$171.49	$171.50	$171.50
Purchase #2	$246.60	13.813%	$280.6629	$280.66	$280.65	$280.70
Purchase #3	$127.66	7.255%	$136.9217	$136.92	$136.90	$136.90
Purchase #4	$167.86	10.122%	$184.8508	$184.85	$184.85	$184.90
Purchase #5	$79.34	3.871%	$82.4113	$82.41	$82.40	$82.40
Purchase #6	$64.34	12.228%	$72.2075	$72.21	$72.20	$72.20
Purchase #7	$153.86	6.643%	$164.0809	$164.08	$164.10	$164.10
7 purchase totals =	$1,002.40		$1,092.6289	$1,092.62	$1,092.60	$1,092.70