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	$122.79	13.424%	$139.2733	$139.27	$139.25	$139.30
Purchase #2	$158.86	13.619%	$180.4951	$180.50	$180.50	$180.50
Purchase #3	$124.83	11.233%	$138.8522	$138.85	$138.85	$138.90
Purchase #4	$209.35	5.756%	$221.4002	$221.40	$221.40	$221.40
Purchase #5	$248.61	8.558%	$269.886	$269.89	$269.90	$269.90
Purchase #6	$17.87	9.297%	$19.5314	$19.53	$19.55	$19.50
Purchase #7	$150.27	5.694%	$158.8264	$158.83	$158.85	$158.80
7 purchase totals =	$1,032.58		$1,128.2646	$1,128.27	$1,128.30	$1,128.30