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	$206.27	8.243%	$223.2728	$223.27	$223.25	$223.30
Purchase #2	$132.84	13.298%	$150.5051	$150.51	$150.50	$150.50
Purchase #3	$46.62	6.708%	$49.7473	$49.75	$49.75	$49.70
Purchase #4	$141.53	6.487%	$150.7111	$150.71	$150.70	$150.70
Purchase #5	$93.87	6.223%	$99.7115	$99.71	$99.70	$99.70
Purchase #6	$134.61	3.646%	$139.5179	$139.52	$139.50	$139.50
Purchase #7	$34.63	13.650%	$39.357	$39.36	$39.35	$39.40
7 purchase totals =	$790.37		$852.8227	$852.83	$852.75	$852.80