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	$69.83	12.779%	$78.7536	$78.75	$78.75	$78.80
Purchase #2	$138.54	3.501%	$143.3903	$143.39	$143.40	$143.40
Purchase #3	$38.78	9.109%	$42.3125	$42.31	$42.30	$42.30
Purchase #4	$220.88	13.440%	$250.5663	$250.57	$250.55	$250.60
Purchase #5	$102.62	3.242%	$105.9469	$105.95	$105.95	$105.90
Purchase #6	$231.86	4.456%	$242.1917	$242.19	$242.20	$242.20
Purchase #7	$61.98	7.587%	$66.6824	$66.68	$66.70	$66.70
7 purchase totals =	$864.49		$929.8437	$929.84	$929.85	$929.90