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	$87.57	3.107%	$90.2908	$90.29	$90.30	$90.30
Purchase #2	$71.28	13.764%	$81.091	$81.09	$81.10	$81.10
Purchase #3	$33.92	13.807%	$38.6033	$38.60	$38.60	$38.60
Purchase #4	$163.68	4.804%	$171.5432	$171.54	$171.55	$171.50
Purchase #5	$99.95	11.630%	$111.5742	$111.57	$111.55	$111.60
Purchase #6	$29.90	4.448%	$31.23	$31.23	$31.25	$31.20
Purchase #7	$43.39	12.389%	$48.7656	$48.77	$48.75	$48.80
7 purchase totals =	$529.69		$573.0981	$573.09	$573.10	$573.10