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	$70.95	13.434%	$80.4814	$80.48	$80.50	$80.50
Purchase #2	$32.63	11.709%	$36.4506	$36.45	$36.45	$36.50
Purchase #3	$73.53	6.285%	$78.1514	$78.15	$78.15	$78.20
Purchase #4	$95.29	7.735%	$102.6607	$102.66	$102.65	$102.70
Purchase #5	$11.85	13.290%	$13.4249	$13.42	$13.40	$13.40
Purchase #6	$149.78	11.314%	$166.7261	$166.73	$166.75	$166.70
Purchase #7	$175.26	11.854%	$196.0353	$196.04	$196.05	$196.00
7 purchase totals =	$609.29		$673.9304	$673.93	$673.95	$674.00