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	$74.66	4.567%	$78.0697	$78.07	$78.05	$78.10
Purchase #2	$55.50	7.355%	$59.582	$59.58	$59.60	$59.60
Purchase #3	$93.97	12.622%	$105.8309	$105.83	$105.85	$105.80
Purchase #4	$235.59	4.705%	$246.6745	$246.67	$246.65	$246.70
Purchase #5	$205.58	8.773%	$223.6155	$223.62	$223.60	$223.60
Purchase #6	$68.72	13.674%	$78.1168	$78.12	$78.10	$78.10
Purchase #7	$83.81	3.189%	$86.4827	$86.48	$86.50	$86.50
7 purchase totals =	$817.83		$878.3721	$878.37	$878.35	$878.40