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	$53.62	4.201%	$55.8726	$55.87	$55.85	$55.90
Purchase #2	$103.42	5.801%	$109.4194	$109.42	$109.40	$109.40
Purchase #3	$48.97	12.871%	$55.2729	$55.27	$55.25	$55.30
Purchase #4	$95.93	13.479%	$108.8604	$108.86	$108.85	$108.90
Purchase #5	$113.85	12.843%	$128.4718	$128.47	$128.45	$128.50
Purchase #6	$169.65	10.412%	$187.314	$187.31	$187.30	$187.30
Purchase #7	$139.43	3.806%	$144.7367	$144.74	$144.75	$144.70
7 purchase totals =	$724.87		$789.9478	$789.94	$789.85	$790.00