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	$231.30	6.516%	$246.3715	$246.37	$246.35	$246.40
Purchase #2	$113.89	6.156%	$120.9011	$120.90	$120.90	$120.90
Purchase #3	$165.81	11.292%	$184.5333	$184.53	$184.55	$184.50
Purchase #4	$9.72	13.739%	$11.0554	$11.06	$11.05	$11.10
Purchase #5	$147.83	9.834%	$162.3676	$162.37	$162.35	$162.40
Purchase #6	$206.97	8.228%	$223.9995	$224.00	$224.00	$224.00
Purchase #7	$78.93	13.747%	$89.7805	$89.78	$89.80	$89.80
7 purchase totals =	$954.45		$1,039.0089	$1,039.01	$1,039.00	$1,039.10