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	$100.44	11.292%	$111.7817	$111.78	$111.80	$111.80
Purchase #2	$52.87	13.300%	$59.9017	$59.90	$59.90	$59.90
Purchase #3	$216.82	6.610%	$231.1518	$231.15	$231.15	$231.20
Purchase #4	$84.26	6.630%	$89.8464	$89.85	$89.85	$89.80
Purchase #5	$36.58	11.274%	$40.704	$40.70	$40.70	$40.70
Purchase #6	$109.92	4.291%	$114.6367	$114.64	$114.65	$114.60
Purchase #7	$177.29	5.736%	$187.4594	$187.46	$187.45	$187.50
7 purchase totals =	$778.18		$835.4817	$835.48	$835.50	$835.50