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	$71.51	12.236%	$80.26	$80.26	$80.25	$80.30
Purchase #2	$109.31	13.353%	$123.9062	$123.91	$123.90	$123.90
Purchase #3	$88.67	5.851%	$93.8581	$93.86	$93.85	$93.90
Purchase #4	$59.83	3.769%	$62.085	$62.09	$62.10	$62.10
Purchase #5	$77.32	5.493%	$81.5672	$81.57	$81.55	$81.60
Purchase #6	$57.25	5.270%	$60.2671	$60.27	$60.25	$60.30
Purchase #7	$190.39	10.636%	$210.6399	$210.64	$210.65	$210.60
7 purchase totals =	$654.28		$712.5835	$712.60	$712.55	$712.70