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	$12.99	7.224%	$13.9284	$13.93	$13.95	$13.90
Purchase #2	$179.57	7.790%	$193.5585	$193.56	$193.55	$193.60
Purchase #3	$120.66	13.620%	$137.0939	$137.09	$137.10	$137.10
Purchase #4	$92.51	13.649%	$105.1367	$105.14	$105.15	$105.10
Purchase #5	$209.29	5.339%	$220.464	$220.46	$220.45	$220.50
Purchase #6	$222.67	8.262%	$241.067	$241.07	$241.05	$241.10
Purchase #7	$78.63	13.629%	$89.3465	$89.35	$89.35	$89.30
7 purchase totals =	$916.32		$1,000.5950	$1,000.60	$1,000.60	$1,000.60