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	$79.93	4.726%	$83.7075	$83.71	$83.70	$83.70
Purchase #2	$80.71	3.278%	$83.3557	$83.36	$83.35	$83.40
Purchase #3	$161.81	10.306%	$178.4861	$178.49	$178.50	$178.50
Purchase #4	$77.59	6.413%	$82.5658	$82.57	$82.55	$82.60
Purchase #5	$5.34	5.141%	$5.6145	$5.61	$5.60	$5.60
Purchase #6	$86.74	3.390%	$89.6805	$89.68	$89.70	$89.70
Purchase #7	$45.50	3.205%	$46.9583	$46.96	$46.95	$47.00
7 purchase totals =	$537.62		$570.3684	$570.38	$570.35	$570.50