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	$138.89	11.139%	$154.361	$154.36	$154.35	$154.40
Purchase #2	$136.86	3.398%	$141.5105	$141.51	$141.50	$141.50
Purchase #3	$48.43	7.293%	$51.962	$51.96	$51.95	$52.00
Purchase #4	$82.96	6.171%	$88.0795	$88.08	$88.10	$88.10
Purchase #5	$225.32	11.301%	$250.7834	$250.78	$250.80	$250.80
Purchase #6	$209.46	11.442%	$233.4264	$233.43	$233.45	$233.40
Purchase #7	$45.60	10.595%	$50.4313	$50.43	$50.45	$50.40
7 purchase totals =	$887.52		$970.5541	$970.55	$970.60	$970.60