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	$148.40	5.405%	$156.421	$156.42	$156.40	$156.40
Purchase #2	$182.34	7.542%	$196.0921	$196.09	$196.10	$196.10
Purchase #3	$66.94	9.626%	$73.3836	$73.38	$73.40	$73.40
Purchase #4	$146.93	11.573%	$163.9342	$163.93	$163.95	$163.90
Purchase #5	$122.61	4.574%	$128.2182	$128.22	$128.20	$128.20
Purchase #6	$86.72	3.732%	$89.9564	$89.96	$89.95	$90.00
Purchase #7	$151.52	12.866%	$171.0146	$171.01	$171.00	$171.00
7 purchase totals =	$905.46		$979.0201	$979.01	$979.00	$979.00