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	$40.38	3.232%	$41.6851	$41.69	$41.70	$41.70
Purchase #2	$207.78	6.384%	$221.0447	$221.04	$221.05	$221.00
Purchase #3	$109.91	4.174%	$114.4976	$114.50	$114.50	$114.50
Purchase #4	$171.57	8.445%	$186.0591	$186.06	$186.05	$186.10
Purchase #5	$47.58	10.326%	$52.4931	$52.49	$52.50	$52.50
Purchase #6	$42.66	5.516%	$45.0131	$45.01	$45.00	$45.00
Purchase #7	$176.81	4.686%	$185.0953	$185.10	$185.10	$185.10
7 purchase totals =	$796.69		$845.8880	$845.89	$845.90	$845.90