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	$59.33	8.567%	$64.4128	$64.41	$64.40	$64.40
Purchase #2	$130.87	9.709%	$143.5762	$143.58	$143.60	$143.60
Purchase #3	$200.38	7.537%	$215.4826	$215.48	$215.50	$215.50
Purchase #4	$176.60	4.679%	$184.8631	$184.86	$184.85	$184.90
Purchase #5	$42.37	12.298%	$47.5807	$47.58	$47.60	$47.60
Purchase #6	$136.37	7.860%	$147.0887	$147.09	$147.10	$147.10
Purchase #7	$12.95	4.604%	$13.5462	$13.55	$13.55	$13.50
7 purchase totals =	$758.87		$816.5503	$816.55	$816.60	$816.60