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	$202.98	7.555%	$218.3151	$218.32	$218.30	$218.30
Purchase #2	$131.71	4.291%	$137.3617	$137.36	$137.35	$137.40
Purchase #3	$238.71	9.562%	$261.5355	$261.54	$261.55	$261.50
Purchase #4	$105.69	10.439%	$116.723	$116.72	$116.70	$116.70
Purchase #5	$222.47	9.779%	$244.2253	$244.23	$244.25	$244.20
Purchase #6	$19.67	11.565%	$21.9448	$21.94	$21.95	$21.90
Purchase #7	$78.61	13.285%	$89.0533	$89.05	$89.05	$89.10
7 purchase totals =	$999.84		$1,089.1587	$1,089.16	$1,089.15	$1,089.10