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	$127.80	3.398%	$132.1426	$132.14	$132.15	$132.10
Purchase #2	$210.27	9.683%	$230.6304	$230.63	$230.65	$230.60
Purchase #3	$76.91	4.575%	$80.4286	$80.43	$80.45	$80.40
Purchase #4	$223.29	3.167%	$230.3616	$230.36	$230.35	$230.40
Purchase #5	$94.63	3.718%	$98.1483	$98.15	$98.15	$98.10
Purchase #6	$168.89	7.696%	$181.8878	$181.89	$181.90	$181.90
Purchase #7	$114.29	12.466%	$128.5374	$128.54	$128.55	$128.50
7 purchase totals =	$1,016.08		$1,082.1367	$1,082.14	$1,082.20	$1,082.00