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	$118.36	5.161%	$124.4686	$124.47	$124.45	$124.50
Purchase #2	$40.75	12.748%	$45.9448	$45.94	$45.95	$45.90
Purchase #3	$200.41	8.524%	$217.4929	$217.49	$217.50	$217.50
Purchase #4	$66.36	6.308%	$70.546	$70.55	$70.55	$70.50
Purchase #5	$17.42	9.223%	$19.0266	$19.03	$19.05	$19.00
Purchase #6	$113.38	6.759%	$121.0434	$121.04	$121.05	$121.00
Purchase #7	$52.77	12.830%	$59.5404	$59.54	$59.55	$59.50
7 purchase totals =	$609.45		$658.0627	$658.06	$658.10	$657.90