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	$121.83	5.208%	$128.1749	$128.17	$128.15	$128.20
Purchase #2	$202.41	10.619%	$223.9039	$223.90	$223.90	$223.90
Purchase #3	$107.77	7.779%	$116.1534	$116.15	$116.15	$116.20
Purchase #4	$96.35	6.161%	$102.2861	$102.29	$102.30	$102.30
Purchase #5	$86.34	9.670%	$94.6891	$94.69	$94.70	$94.70
Purchase #6	$165.57	5.331%	$174.3965	$174.40	$174.40	$174.40
Purchase #7	$242.30	6.819%	$258.8224	$258.82	$258.80	$258.80
7 purchase totals =	$1,022.57		$1,098.4263	$1,098.42	$1,098.40	$1,098.50