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	$75.85	9.297%	$82.9018	$82.90	$82.90	$82.90
Purchase #2	$219.73	10.216%	$242.1776	$242.18	$242.20	$242.20
Purchase #3	$72.55	5.727%	$76.7049	$76.70	$76.70	$76.70
Purchase #4	$166.84	3.375%	$172.4709	$172.47	$172.45	$172.50
Purchase #5	$164.51	6.389%	$175.0205	$175.02	$175.00	$175.00
Purchase #6	$246.41	13.807%	$280.4318	$280.43	$280.45	$280.40
Purchase #7	$246.64	3.340%	$254.8778	$254.88	$254.90	$254.90
7 purchase totals =	$1,192.53		$1,284.5853	$1,284.58	$1,284.60	$1,284.60