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	$137.41	4.247%	$143.2458	$143.25	$143.25	$143.20
Purchase #2	$130.88	4.706%	$137.0392	$137.04	$137.05	$137.00
Purchase #3	$165.33	3.649%	$171.3629	$171.36	$171.35	$171.40
Purchase #4	$197.65	13.587%	$224.5047	$224.50	$224.50	$224.50
Purchase #5	$164.50	4.630%	$172.1164	$172.12	$172.10	$172.10
Purchase #6	$54.62	5.648%	$57.7049	$57.70	$57.70	$57.70
Purchase #7	$156.83	11.173%	$174.3526	$174.35	$174.35	$174.40
7 purchase totals =	$1,007.22		$1,080.3265	$1,080.32	$1,080.30	$1,080.30