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	$76.89	13.403%	$87.1956	$87.20	$87.20	$87.20
Purchase #2	$232.80	13.178%	$263.4784	$263.48	$263.50	$263.50
Purchase #3	$92.82	6.871%	$99.1977	$99.20	$99.20	$99.20
Purchase #4	$10.73	11.187%	$11.9304	$11.93	$11.95	$11.90
Purchase #5	$48.65	9.122%	$53.0879	$53.09	$53.10	$53.10
Purchase #6	$131.48	5.381%	$138.5549	$138.55	$138.55	$138.60
Purchase #7	$171.61	11.262%	$190.9367	$190.94	$190.95	$190.90
7 purchase totals =	$764.98		$844.3816	$844.39	$844.45	$844.40