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	$116.45	9.140%	$127.0935	$127.09	$127.10	$127.10
Purchase #2	$33.64	5.145%	$35.3708	$35.37	$35.35	$35.40
Purchase #3	$163.71	10.787%	$181.3694	$181.37	$181.35	$181.40
Purchase #4	$33.98	12.591%	$38.2584	$38.26	$38.25	$38.30
Purchase #5	$45.62	11.579%	$50.9023	$50.90	$50.90	$50.90
Purchase #6	$47.31	10.822%	$52.4299	$52.43	$52.45	$52.40
Purchase #7	$23.95	13.780%	$27.2503	$27.25	$27.25	$27.30
7 purchase totals =	$464.66		$512.6746	$512.67	$512.65	$512.80