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	$78.61	7.209%	$84.277	$84.28	$84.30	$84.30
Purchase #2	$225.61	5.720%	$238.5149	$238.51	$238.50	$238.50
Purchase #3	$78.36	9.466%	$85.7776	$85.78	$85.80	$85.80
Purchase #4	$198.62	12.197%	$222.8457	$222.85	$222.85	$222.80
Purchase #5	$95.59	13.258%	$108.2633	$108.26	$108.25	$108.30
Purchase #6	$246.80	9.329%	$269.824	$269.82	$269.80	$269.80
Purchase #7	$34.48	3.495%	$35.6851	$35.69	$35.70	$35.70
7 purchase totals =	$958.07		$1,045.1876	$1,045.19	$1,045.20	$1,045.20