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	$201.59	9.680%	$221.1039	$221.10	$221.10	$221.10
Purchase #2	$89.94	8.302%	$97.4068	$97.41	$97.40	$97.40
Purchase #3	$72.64	10.703%	$80.4147	$80.41	$80.40	$80.40
Purchase #4	$113.49	5.365%	$119.5787	$119.58	$119.60	$119.60
Purchase #5	$128.97	4.562%	$134.8536	$134.85	$134.85	$134.90
Purchase #6	$81.40	9.646%	$89.2518	$89.25	$89.25	$89.30
Purchase #7	$47.50	13.240%	$53.789	$53.79	$53.80	$53.80
7 purchase totals =	$735.53		$796.3985	$796.39	$796.40	$796.50