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	$239.95	10.792%	$265.8454	$265.85	$265.85	$265.80
Purchase #2	$40.78	9.421%	$44.6219	$44.62	$44.60	$44.60
Purchase #3	$221.40	6.311%	$235.3726	$235.37	$235.35	$235.40
Purchase #4	$181.76	9.276%	$198.6201	$198.62	$198.60	$198.60
Purchase #5	$59.78	10.839%	$66.2596	$66.26	$66.25	$66.30
Purchase #6	$135.98	4.755%	$142.4458	$142.45	$142.45	$142.40
Purchase #7	$48.88	3.590%	$50.6348	$50.63	$50.65	$50.60
7 purchase totals =	$928.53		$1,003.8002	$1,003.80	$1,003.75	$1,003.70