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	$166.26	7.649%	$178.9772	$178.98	$179.00	$179.00
Purchase #2	$78.89	3.437%	$81.6014	$81.60	$81.60	$81.60
Purchase #3	$136.80	5.809%	$144.7467	$144.75	$144.75	$144.70
Purchase #4	$238.84	12.132%	$267.8161	$267.82	$267.80	$267.80
Purchase #5	$44.87	13.673%	$51.0051	$51.01	$51.00	$51.00
Purchase #6	$70.57	11.674%	$78.8083	$78.81	$78.80	$78.80
Purchase #7	$66.26	9.469%	$72.5342	$72.53	$72.55	$72.50
7 purchase totals =	$802.49		$875.4890	$875.50	$875.50	$875.40